It is assumed that relational factors play an important role in psychotherapy (Wampold and Imel, 2015). The therapeutic alliance and related factors have been shown to significantly predict treatment outcome in adult psychotherapy (e.g., Flückiger et al., 2018). A similar argument can be made for psychotherapy with children and adolescents. For example, Kernberg et al. (2012) proposed recommendations for child psychotherapy, some of which deal with the therapeutic alliance. These emphasize that in order to create a safe psychotherapeutic space and promote appropriate alliance-building, therapists should carefully consider the child’s developmental level and personality structure within a setting that ensures respect for the child’s autonomy. A shared understanding of the child’s behavior/symptoms should also be developed with parents or caregivers. Analogously, it has been stated that the work with adolescents poses particular challenges in the adequate building of the therapeutic alliance because these latter, because of their developmental stage, tend to minimize psychological problems (Shirk and Saiz, 1992) and mistrust adult authority (DiGiuseppe et al., 1996), thus complicating the engagement in the therapeutic relationship.

In a qualitative study of children’s experiences of their therapeutic relationship, Baylis et al. (2011) developed an empirically informed process model of the psychotherapeutic alliance with children (Child Alliance Process Theory). Such a model posits that the therapeutic alliance with children develops in layers (for an example in adult psychotherapy, see Gelo et al., 2016). First, therapists engage the child in the relationship by proposing activities, expressing care, listening actively, and attending to ruptures. Then, therapists strengthen the building alliance by further proposing activities, demonstrating patience, validating feelings, and respecting privacy and confidentiality. These findings appear to be supported by another qualitative study that longitudinally examined the child-therapist and parent-therapist relationships as agents of change from the perspectives of children, parents, and therapists (Núñez et al., 2022). The results showed that the therapeutic relationship in the early sessions facilitated change by allowing children’s reticence to be addressed, thereby improving their positive attitudes toward therapy; supporting children’s intrapersonal changes through the opportunity for positive interactions; and increasing parents’ confidence in the therapist’s ability to overcome the challenges initially presented by the child. However, in later stages of treatment, the therapeutic relationship facilitated change by allowing the children to become increasingly involved in the therapeutic process and to feel accepted and free by the therapist, leading the children to feel that the therapist helped them to change; facilitated cooperative engagement of therapists and parents, for the former through a flexible and child-centered attitude, for the latter through the therapist’s ability to establish an affective relationship with the children.

Concerning quantitative research, meta-analyses support a relevant (small to medium) effect of the therapeutic alliance on outcome in psychotherapy for children and adolescents, including PPCA (Karver et al., 2006, 2018; Shirk and Karver, 2003; Shirk et al., 2011). At a more specific level, Halfon et al. (2019a) found that the therapeutic alliance in child psychodynamic therapy has a high-low-high time course, with children with internalizing and externalizing problems showing a decreasing and increasing alliance curve, respectively. In addition, the time course of the overall alliance predicted treatment outcome. Halfon (2021) showed that psychodynamic techniques in psychodynamic child psychotherapy best predicted treatment outcome when used in the context of a high therapeutic alliance. Similar results were found by Ramires et al. (2022).

Other empirical studies examined specific elements of the psychotherapeutic relationship and their association with treatment outcome in PPCA. Atzil-Slonim et al. (2015) showed that adolescents developed both positive and negative internal representations of their therapeutic relationship over the treatment, with an increase in the former and a decrease in the latter being associated with greater treatment satisfaction. Moreover, the development of these relational representations was associated with an improved perception of the relationship with parents. These findings are particularly significant in that they support the idea that in PPCA, work in the here and now can facilitate the development of new interpersonal representations of the therapist in the client, which in turn affect other important relationships (Atzil-Slonim et al., 2015). In another study, Halfon et al. (2018) identified four interaction structures in psychodynamic child psychotherapy using the Child Psychotherapy Q-Set: therapeutic alliance, children’s emotional expression, child-centered techniques, and psychodynamic technique. Although the therapeutic alliance factor explained the highest variance in the data set, it was not found to predict outcome (along with children’s emotional expression).

Some studies have focused on the contribution of pre-treatment characteristics or in-session behaviors to alliance development in therapeutic approaches other than psychodynamic. Regarding the former, for example, it has been found that adolescent maltreatment experiences and severity of interpersonal problems predict, respectively, difficulties in initial alliance formation and alliance development and, consequently, poorer outcome (Eltz et al., 1995; see also Colson et al., 1991). Regarding the latter, some studies have shown that the development of the therapeutic alliance is associated with therapists paying attention to the youths’ personal experience, setting meaningful goals, and presenting themselves as allies in adolescent family therapy (Diamond et al., 1999), the use of a collaborative language in child cognitive-behavioral therapy (Creed and Kendall, 2005). Moreover, Russell et al. (2008) found that the development over time of therapists’ responsivity, experiential socialization, and remoralization predict subsequent therapist and client-rated alliance in cognitive-behavioral therapy for adolescents. Although promising, these findings suggest that the role of the therapeutic alliance and other relational factors in the change process of PPCA needs to be further examined in the future.

The general literature on common factors often mentions the following patient factors: active help-seeking and willingness to participate, motivation and readiness for change, therapy involvement, positive expectations, hope, and belief in treatment (e.g., Tracey et al., 2003). These factors also seem to play a relevant role in the psychodynamic treatment of children and adolescents. Active seeking of help and willingness to participate play a relevant role in PPCA, as shown by a meta-analysis of Karver et al. (2006) reporting medium effects of willingness to participate on treatment outcome. This is further related to children and adolescents’ motivation and readiness for change as important factors in PPCA. Some empirical research has been conducted in this regard, showing that young people with higher motivation and commitment to therapy develop better therapeutic alliance (Ellis et al., 2012; Estrada and Russell, 1999; Fitzpatrick and Irannejad, 2008) and may have better outcomes (Black and Chung, 2014; Adelman et al., 1984; for contrary results, see Killips et al., 2012). The same can be said concerning children and adolescents’ treatment involvement, as shown by a meta-analysis of Karver et al. (2006), which found a moderate effect of actual participation in therapy on treatment outcome.

Positive expectations and hope of children and adolescents are given relatively little attention in the literature on PPCA and are also not reflected in treatment manuals. However, its relevance has been emphasized by the development of the Hopes and Expectations for Treatment Approach (HETA; Urwin, 2009) as an assessment tool to evaluate child psychotherapy’s effectiveness. In a mixed-methods investigation of the expectations and experiences of children treated with psychodynamic psychotherapy, Carlberg (2009) found that the majority of the children expressed positive expectations and hopes regarding the treatment before it started and, after termination, considered their therapy experience as positive or very positive. However, a survey of young clients by Watsford and Rickwood (2014) did not find a relationship between their initial expectation and treatment outcome, even though the latter was predicted by clients’ experience of therapy and their preference for personal engagement in therapy. This area certainly needs further research. Despite these promising results, there is a need for further empirical research on the role of patient factors in the change process of children and adolescents’ psychotherapy change processes.

Sprenkle et al. (2013) underline that the person of the psychotherapist plays a fundamental role in the psychotherapeutic alliance: Therapists differ as people not just in what they do but also in who they are. Clients react to therapists as therapists but also as people. A therapist has an age, a gender, a culture, a way of speaking and being. “(p. 92). With this regard, so-called interpersonal skills (i.e., empathy, warmth, and genuineness) are considered to play a pivotal role in psychotherapy, especially in relation to the possibility of building and managing an adequate therapeutic alliance (e.g., see Grencavage and Norcross, 1990; Tracey et al., 2003). The therapist’s intersubjective ability to recognize their own and others’ internal states and to understand the development of the relationship between them and the patients are of great importance in this respect (e.g., see Grencavage and Norcross, 1990; Tracey et al., 2003).

These factors may also be relevant in PPCA. In one seminal study investigating therapists’ interpersonal skills as predictors of outcome in child therapy, Truax et al. (1973) showed that high therapist’s empathy, warmth, and genuineness produced greater behavior and personality change, while low levels of these variables produced even a worsening of the children condition. More than 30 years later, the meta-analysis conducted by Karver et al. (2006) produced analogous results. The same meta-analysis showed that therapists’ direct influence skills (e.g., providing an active structure to the session, a rationale for the treatment, and instructions and guidance) also positively impact treatment outcome (Karver et al., 2006).

Such influence skills have also been shown to enhance therapist credibility (i.e., the extent to which they are perceived attractive, trustworthy, and having expertise) (Hoyt, 1996). Therapist credibility is supposed to instill positive expectations, hope, and faith in the client (Frank and Frank, 1991), thus positively influencing treatment process and outcome (for a meta-analysis on adult psychotherapy, see Hoyt, 1996). However, although there have been some empirical investigations exists in children and adolescents psychotherapy (e.g., Stein et al., 2001), more empirical research is needed.

The following therapeutic factors also play a relevant role in the treatment of children and adolescents. First, the ability to involve and triangulate with parents, that is, the ability to build and manage different relationships with the patient’s family members and to analyze how these relate to the client’s relationship patterns with the therapist (Hanley and Noble, 2017; for a review, see Ruberman, 2009). The modality and frequency of contacts may depend on the patient’s developmental stage and is crucial, especially for children. From the beginning, the therapist must make explicit to the child or adolescent the nature and meaning of this parental involvement in a shared, clear, and transparent way (Kernberg, 2006). Such involvement has the primary function of gaining parental cooperation by clarifying treatment goals and strategies, which in turn is essential for establishing and maintaining a therapeutic setting (e.g., Kehr and Köpp, 2018). It may also be useful in gathering information about specific events concerning the patient or more general family dynamics, which in turn may be useful in therapeutic work with the child/adolescent. In addition, the therapist may provide psychoeducational support to parents, for example, by trying to facilitate their understanding of the patient’s situation and/or promoting parenting skills (e.g., Martinez et al., 2017). The therapist can provide emotional containment to parents in times of particular need. Second, the therapist’s ability to play. Psychotherapists who work with children must be able to engage and be engaged in a game or allow themselves to be used as an object in the game (Kernberg et al., 2012; see the later section on play in this article). Third, flexibility, which in working with children and adolescents refers to the ability to evaluate the nature and timing of interventions according to the patient’s developmental stage (Karver et al., 2005). A final therapist factor we would like to address is allegiance (i.e., the extent to which the therapist believes the therapy is effective) (Wampold and Imel, 2015), which has been suggested as a common factor that plays a relevant role in determining treatment effectiveness. Unfortunately, the authors could not locate any empirical research on these therapist factors.

Parents’ participation, expectations, and motivations positively influence treatment outcome (Karver et al., 2005). The importance of involving parents is illustrated, for example, by a meta-analysis showing that both parents’ willingness to participate in treatment predict therapy outcome (Karver et al., 2006). More specifically, it has been found that the severity of children’s behavioral problems and degree of parental distress reduces the within-session involvement of parents (Haine-Schlagel et al., 2012), which in turn can be promoted by in-session parental psychoeducation (e.g., discussing the child problem causes and providing a treatment rationale) (Martinez et al., 2017). In addition, Kazdin and Wassell (2000) found that the extent to which parents perceived barriers to treatment participation and therapeutic change was associated with their perceptions of treatment relevance and outcome. Further, the perception of both treatment barriers and change was predicted by parental psychopathology and lower levels of quality of life (see also Fonagy and Target, 1995).

Nock and Kazdin (2001) investigated parental expectations of therapy, finding that these predict treatment barriers, attendance, and premature termination. With this regard, Shuman and Shapiro (2002) showed that providing parents with preliminary information about psychotherapy increases the accuracy of their treatment expectations and, at least to a minimal extent, treatment attendance.

In the treatment of children and adolescents, family dynamics (e.g., intergenerational conflicts, family role allocation, parenting practices, interplay between attachment styles, parental relationship experiences, ego strengths, and triangulation skills of the parents as well as their introspection and interpersonal) may also play a relevant role (e.g., Möhring, 1999). There has been no specific empirical research on this in psychotherapy with children and adolescents, except for parenting practices (see Kennedy and Midgley, 2007; Ng et al., 2021).

Another important common factor regards the parent-therapist therapeutic alliance, which, analogously to the client-therapist alliance, involves an emotional bond and agreement on goals and tasks between the parents and the therapist (see Accurso et al., 2013). Two qualitative studies by Núñez et al. (2021, 2022) investigated how the triadic (parents, child, and therapist) dynamic nature of the therapeutic relationship influences the change process. The results indicated that the therapist’s commitment and playful stance, as well as the parents’ close and adaptable attitude, collaboration, and mutual involvement between child and therapist within a caring, validating, and trustful relationship, influenced the parents’ and children’s motivation and facilitated change and the development of socio-affective tools.

One of the first meta-analyses on parent-therapist alliance estimated a relatively small effect on patient change (Karver et al., 2006). Analogous results were produced by a later meta-analysis by McLeod (2011). In line with this, other empirical studies suggest that while the child-therapist alliance seems to be more associated with client change, the parent-therapist alliance seems more associated with treatment continuation and lower levels of dropout (Kazdin et al., 1997; Weisz et al., 2005; Zack et al., 2007 see also Hawley and Weisz, 2005).

Finally, regarding the broader interpersonal environment of the patient, it has been shown that social support predicts higher patient-therapist therapeutic alliance (Shirk and Karver, 2003) and treatment outcome (Black and Chung, 2014). Analogously, interpersonal problems in social relationships predicted difficulties in establishing an adequate therapeutic relationship (Eltz et al., 1995).

Mentalizing (or reflective function; RF) can be defined as the metacognitive ability „to understand others’ and one’s behavior in terms of mental states “(Fonagy and Allison, 2014, p. 1). It has been shown that its development fundamentally contributes to adaptive socio-emotional-cognitive outcomes (Schore, 2014), while a lack of mentalizing is related to several psychopathological conditions (Bateman and Fonagy, 2012; for a social constructionist account of psychopathology, see Gelo et al., 2015b). Although mentalizing has also been conceptualized as a treatment outcome, an increasing number of scholars suggest it represents a therapeutic factor (for an empirical review, see Katznelson, 2014). Moreover, although this concept originates within the psychodynamic tradition and is explicitly implemented in mentalization-based treatments for adults (Bateman, 2022) and children (Lindqvist et al., 2023), the relevance of such a construct as a common therapeutic factor is emphasized by an increasing amount of scholars (Bateman et al., 2018; Fonagy and Allison, 2014; Montgomery-Graham, 2016). As stated by Goodman et al. (2016), “If this hypothesis is valid, then various treatment models are effective because they revive the patient’s capacity to interpret behavior as motivated by the underlying mental states of self and other” (p. 3; see also Bateman and Fonagy, 2017), with different models enhancing/focusing on various dimensions mentalizations (self/other, implicit/explicit, affective/cognitive).

From this perspective, it has been suggested that it is fundamental for child and adolescent therapists to adopt a mentalizing attitude or stance (also called RF approach) (Fonagy and Adshead, 2012). Muñoz Specht et al. (2016) developed a conceptual framework of mentalization-based interventions through a qualitative study of the sessions of two experienced child and adolescent psychodynamic psychotherapists. An overall mentalizing stance principle emerged, which entailed the “therapist’s orientation toward the patient’s inner world” (p. 289). This comprised interventions aimed at promoting the patient’s exploration and emotional expressions of their inner states and the development of alternative perspectives regarding the self, the other, and their relationship within an empathic, caring, supportive, and self-reflecting relationship both within and outside the play context. Some studies have been conducted on the therapist RF approach in child and adolescent psychotherapy, showing its association with therapeutic alliance, symbolic play, and affect regulation (Halfon and Bulut, 2017; Halfon et al., 2017b; Ramires et al., 2022) as well as with treatment outcome (Halfon et al., 2019b).

Analogous results have been found concerning the patient’s mentalizing abilities. For example, Ramires et al. (2022) found that increased children’s RF abilities positively impact patient-therapist interaction structures. Similarly, it was shown that while lower baseline levels of children’s RF correlate with more problematic behaviors, an increase in children’s RF is associated with treatment outcome (Oehlman Forbes et al., 2021). Finally, it can be argued that also parents’ mentalizing can be a relevant factor in child and adolescent psychotherapy. For example, Halfon and Besiroglu (2021) found that parents’ RF predicted a reduction in children’s problematic behavior over treatment. Although most of the studies indicated above (these studies) have been conducted in the context of psychodynamic approaches, research employing the Child Psychotherapy Q-set (Schneider, 2003) has shown that a focus on mentalization characterizes not only PPCA (e.g., Carvalho et al., 2019; Di Lorenzo et al., 2015) but also other child and adolescents’ psychotherapeutic approaches [e.g., cognitive-behavioral (Goodman et al., 2016) and child-centered (Prout et al., 2018) child therapy]. Overall, the existing results are promising. However, further empirical research is needed to assess better the role of mentalizing in child and adolescent psychotherapy.

Although the relevance of play in the therapeutic process of child psychotherapy has been originally emphasized in the psychodynamic tradition (see a previous section in the present paper), several other approaches have been increasingly acknowledging the central role of play in promoting change in child psychotherapy (Porter et al., 2009). Notwithstanding the existing differences, it is possible to identify common features characterizing play’s therapeutic role in child psychotherapy. For example, Schaefer and Drewes (2013) developed a transtheoretical play therapy model inspired by humanistic, psychodynamic, and cognitive-behavioral therapy. Such a model identifies 20 therapeutic core agents of play differently related to cognitive, emotional, and interpersonal processes and considered to facilitate communication, foster emotional wellness, and increase personal strengths. As stated by the authors, “play actually helps produce the change and is not just a medium for applying other change agents nor does it just moderate the strength or direction of therapeutic change” (Schaefer and Drewes, 2013, p. 2).

Such a view is consistent with the idea that symbolic play is a facilitator for the development of the child’s ability to mentalize, providing a safe environment for exploring different aspects of one’s own experience and fostering the child’s ability to imagine the inner experiences of play characters, their thoughts, beliefs, intentions, and feelings (Fonagy and Target, 1995; for an account of the developmental and clinical functions of safety and intersubjective mentalizing, see Podolan and Gelo, 2023, 2024). In this context, the play offers the therapist a privileged frame to facilitate the child’s symbolic abilities by identifying the underlying mental states of their behavior during play or verbalizing the desires or intentions of the characters involved in the play and their connections to significant other in the child’s life, such as the parents (Zevalkink et al., 2012). During play, the use of mental discourse by therapists in relation to children’s mental states allows these latter to organize their own experiences so that they have a better understanding of their inner world (Fonagy and Target, 1998); this, in turn, can help them to formulate hypotheses about the link between emotions and behaviors, and then develop the ability to communicate and regulate emotions (Fonagy and Target, 1998).

Several meta-analyses support the effectiveness of play in child psychotherapy (e.g., Drisko et al., 2020). However, only a few empirical investigations have focused on the play process. Beyond some qualitative single-case studies providing preliminary evidence about the relevance of the play process for healing and therapeutic change in child psychotherapy (e.g., Campbell and Knoetze, 2010; Ebenstiner, 1998), quantitative research employing the CPTI (Kernberg et al., 1998) has shown that an increase in children’s symbolic play is associated with or predict better affect regulation (e.g., Halfon and Bulut, 2017; for systematic case studies, see Chari et al., 2013; Chazan and Wolf, 2002), which in turn predict positive treatment outcome (Halfon et al., 2019b) in psychodynamic child psychotherapy. Moreover, Halfon et al. (2017b) found that play offers children the possibility for mental state talk (i.e., words used to attribute inner states to others), and when parents are involved in the play activity, the child’s role-playing ability is associated with both children and mothers’ (but not fathers’) play-related mental state talk. Moreover, there was an association between the child’s affect regulation in play and the mother’s mental state talk, while the ability of children and mothers to verbalize mental states during pretend play was associated with less internalizing problems. On the contrary, out of pretend play, the mental state talks of children, mothers, and fathers were associated with more externalizing problems (see also Halfon et al., 2017a).

A series of systematic case studies employing the Child Psychotherapy Q-Set (CPA; Schneider, 2003) have examined the role of symbolic play in psychodynamic child psychotherapy. Findings showed that symbolic play is positively associated with the therapist’s mentalizing stance and the therapeutic alliance (Ramires et al., 2022) and that play-related processes (e.g., children engaging therapists in play, therapists trying to understand children’s play) are among the characteristic issues of children’s repetitive patterns of interaction (Ramires et al., 2015; see also Ramires et al., 2020). Although these studies were conducted in the context of psychodynamic child therapy, they highlight the extent to which play and related processes can contribute to the process of change in child psychotherapy in general.