The goal of this clinical trial is to optimize a school-based therapeutic play intervention in preschool students with mild to moderate school adjustment difficulties. The aims are:

1. Determine the independent and combined effects of three intervention components (individual play, peer play, and classroom push-in sessions) on preschool children's social and emotional competence, using a factorial experimental design.
2. Use a community-engaged approach to identify and disseminate the optimized version of Primary Project for preschool implementation

Researchers will compare the main and interactive effects of three components on children's social-emotional competencies.

Participants will take part in a therapeutic play intervention in the school setting, and their teachers and caregivers will complete assessment instruments on children's social and emotional functioning.

Background and rationale:

There are a growing number of children in the United States with mental, emotional, or behavioral health concerns (Perou et al., 2013; SAMHSA, 2022). Left untreated, these difficulties may persist through development and contribute to a wide range of negative outcomes in adolescence and adulthood. Consequently, there is a critical need to identify effective strategies that promote protective factors, enhance resiliency, and disrupt the causal processes that facilitate the emergence of subsequent mental health problems. Prevention programs that enhance young children's social and emotional competencies can both alleviate present difficulties and protect youth against future mental health problems (Greenberg et al., 2003; Greenberg et al., 2017).

Early childhood is a critical developmental period for social and emotional growth, with key developmental milestones including the growth of peer social skills and self-regulation abilities. Educational settings are important contexts for fostering young children's social and emotional development. Children who adjust well to the school setting are more apt to thrive in terms of their social and emotional skill development, whereas children who struggle with the transition to the early school years may face challenges across multiple domains (Alzahrani et al., 2019). It is these elevated symptoms detected within the general student population, not diagnoses of specific childhood disorders, that best predict adult mental health outcomes (Mulraney et al., 2021). Consequently, preventive interventions that include universal screening and encourage social and emotional skill development, while also facilitating a positive transition to the educational environment, are ideal.

School-based interventions are well positioned to strengthen children's social and emotional competencies and reduce future risk (National Research Council & Institute of Medicine, 2009). Schools serve as a context for growth in multiple domains of socioemotional development, including interpersonal skill development with peers and adult figures, intrapersonal awareness of academic and non-academic skills, coping with difficulties, and managing the simultaneous demands of curricular and extracurricular activities (Aviles et al., 2006). Further, recent evidence indicates that school-based interventions grounded in child-centered play therapy (CCPT) are related to reductions in children's behavioral, emotional, and academic problems (Ray et al., 2015). There is also some growing evidence that non-clinical preventive interventions grounded in the tenets of CCPT (i.e., Child-Centered Play Interventions; CCPIs) are effective for children's social and emotional development (Perryman & Bowers, 2018). CCPIs are often more feasible and sustainable for schools - for instance, they are facilitated by a specially trained school-based paraprofessional (i.e., child associate) who is supervised by a licensed school-based mental health professional (Peabody et al., 2018). However, research based on CCPIs is limited.

Primary Project is a long-standing CCPI that targets children in kindergarten through third grade (approximately ages 5 - 9) who are having school adjustment difficulties (Johnson et al., 2005; Peabody et al., 2018). The program provides structured play sessions with trained paraprofessional child associates under the supervision of mental health professionals to support children with early school adjustment difficulties. The goals of Primary Project are to enhance school-related social and emotional competencies (e.g., task orientation and peer social skills) while reducing behavioral and interpersonal adjustment difficulties in children.

Prior research has established the effectiveness of Primary Project in improving school adjustment outcomes in young children (see Cowen et al., 1996 for a review) and a recent study demonstrated positive effects on children's school attendance (Lotyczewski et al., 2024). A recent randomized controlled trial supported the program's effectiveness for improving children's social skills and self-regulation (Aaron et al., forthcoming).

Building on this foundation, Primary Project was adapted for preschool-aged children (approximately age 4) by adding developmentally appropriate components, including a greater focus on peer-play skills. The Pre-K Primary Project model includes three core components: individual play sessions, structured peer play sessions, and classroom push-in sessions wherein the paraprofessional child associate provides individual support to the child in a classroom setting. Conceptually, these three components act upon proximal mediators (e.g., increasing emotion regulation skills and self-efficacy; facilitating positive peer relationships; and promoting school connectedness) to enhance children's overall social-emotional adjustment (Figure 1).

However, despite increasing implementation, the Pre-K Primary Project model has not undergone systematic evaluation to understand which components, and in what combination, are most effective. This represents a critical gap given the Pre-K model's multi-component nature. Understanding the individual and combined effects of its components is essential to guide schools towards efficient and sustainable program goals.

The current trial addresses this gap by using the Multiphase Optimization Strategy (MOST), an innovative translational framework (Guastaferro & Pfammatter, 2023) to develop and evaluate multi-component interventions (Collins et al., 2024; Guastaferro & Collins, 2019). MOST involves three phases: preparation, optimization, and evaluation. In the preparation phase, investigators establish a conceptual model, identify candidate intervention components, and define an optimization objective that balances effectiveness with practical constraints. In the optimization phase, the goal is to empirically identify the optimized intervention via a randomized controlled trial (RCT), often using a factorial experimental design. The optimized intervention is the combination of candidate intervention components that achieves the best balance of intervention effectiveness with affordability, scalability, and efficiency (i.e., intervention EASE; Collins et al., 2021) Finally, in the evaluation phase, the optimized intervention package is tested in a RCT, usually in a 2-arm trial, to confirm its effectiveness under real-world conditions compared to a suitable control.

The present trial represents the optimization phase of MOST. The specific optimization goal is to identify the combination of components that are most effective for improving children's social-emotional outcomes and school adjustment, while also being feasible in terms of program timing and resource constraints (e.g., ability to offer two full cycles per school year without incurring additional staffing costs). In sum, this trial examines whether individual play sessions, peer play sessions, and classroom push-ins, independently and in combination, improve preschool children's social-emotional adjustment. The overall goal is to develop an optimized program model for broader dissemination.

Objectives:

The primary objective of this trial is to optimize the Pre-K Primary Project intervention for strengthening preschool children's social-emotional adjustment. The first specific aim of this study is to determine the independent and combined effects of three intervention components (individual play, peer play, and classroom push-in sessions) on preschool children's social and emotional competence, using a factorial experimental design.

As an exploratory sub-aim, we also seek to explore the impact of intervention components on identified mediators including children's level of school connectedness, emotion regulation, and peer relationships. These exploratory analyses will inform iterative revisions to the conceptual model and future research studies.

Our second specific aim is to use a community-engaged approach to identify and disseminate the optimized version of Primary Project for preschool implementation. Specifically, we will work with school partners to consider the results from the optimization trial, balanced with the feasibility, sustainability, and affordability of different intervention packages (e.g., ability to offer two cycles per school year without incurring additional costs from staffing or other resources). These results will be disseminated via a new program manual and other materials targeted to both academic and non-academic audiences.

Inclusion Criteria: Children will be eligible if they are enrolled in preschool classrooms at participating schools and identified as appropriate for intervention through universal screening. Screening will be conducted using the Teacher-Child Rating Scale (T-CRS; Hightower et al., 1986), a teacher-completed measure of social-emotional adjustment. Children who score in the target range indicating emerging adjustment difficulties (i.e., 15th to 30th percentile) will be eligible for participation in the trial.

Exclusion Criteria: Children will be excluded if they demonstrate severe developmental impairments that would prevent participation in the intervention.

The study will protect the confidentiality of all data at all stages. Parents are informed during the consent process that all responses are confidential and are only for research purposes.

Only the investigator and authorized study personnel will have access to identifiable information. Data is stored on password-protected servers compliant with FERPA and all personal identifiers will be removed prior to analysis. Each participant will be assigned an anonymized study identifier.After data collection is complete, only deidentified data will be retained for analysis and long-term storage. These deidentified datasets will be stored on encrypted cloud-based servers with access restricted to the study team.

Data will be reported on in the aggregate, and we will not report on any subgroups with fewer than 10 individuals.