1. Introduction

This assumption is not limited to the familial context and parenting experience, but it comprehends professional care in early childhood education services [5]^[1]. According to the literature, teacher–child interactions represent the most salient component of Early Childhood Education and Care (ECEC) service quality in terms of children’s social-emotional functioning [6]^[2]. Professional caregivers determine the quality of young children’s ordinary experiences in childcare by direct “back-and-forth” interactions [7]^[3], and by mediating relationships with peers and with the school environment [8]^[4]. Through nurturing and supportive relationships, children are sustained in learning, understanding, and regulating their behavior and emotions [4,9]^[5][6]. Children are encouraged by the interaction with the adult caregiver to regulate their emotional response, take part in social interactions, and experience empathy [10]^[7]. Furthermore, positive caregiver–child interactions in the early childcare setting are associated with children’s improved cognitive development and reduced behavioral problems in primary school [11^[8][9],12], and with their environmental adjustment and academic success at school age [13,14]^[10][11].

The Teaching Through Interactions (TTI) Framework theorized by Hamre and Pianta [7]^[3], identifies three broad domains of teacher–child interactions which are considered effective in promoting children’s development and learning process, together with their socioemotional skills: (a) emotional support, (b) classroom organization, and (c) instructional support. The dimension of Emotional Support (ES) is associated with consistent, positive, and sensitive relationships between children and teachers. It includes the warmth and respect displayed in teacher–child interactions, the enjoyment shown during learning activities, the positive and negative effects expressed within the group of children, the teachers’ responsivity and sensitivity, and teachers’ flexibility within activities to respect children interests and autonomy. Classroom Organization (CO) refers to adults’ effective capability to manage children’s behavior in the school environment, structuring everyday routines, and sustaining learning processes. Finally, the dimension of Instructional Support (IS), deeply related to academic success, is assessed in terms of the quality of teachers’ feedback or the use of instructional strategies that encourage higher-order thinking [15]^[12].

The TTI dimensions have been translated into professional learning and evaluated in several intervention studies to sustain caregiver–child interaction in the early childhood education context [11,16,17]^[8][13][14]. However, while results from these studies showed improvements in teachers knowledge, skills, and children outcomes, researchers did not reach strong conclusions about the effective elements of caregiver trainings due to heterogeneity in the focus, design, and implementation of these programs [11]^[8]. In addition to this, while several programs focusing on improving children’s cognitive school readiness have been designed and implemented, interventions targeting the caregiver–child relationship and children’s socio-emotional development have been less investigated [11]^[8]. Over recent decades, policies across The Organization for Economic Co-operation and Development (OECD) countries are beginning to recognize the important role of warm and supportive relationships with teachers, peer engagement, and teachers’ strategies during play and structured group time in fostering children’s socioemotional development [18]^[15]. The social and emotional competencies developed in early childhood are extremely important because they act as the foundation for ongoing health, wellbeing, prosocial relationships, and engagement in learning during primary school.

2. Reference

In planning, conducting, and reporting on this study, we followed the guidelines from the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [20]^[16]. Strong heterogeneity in both the studies themselves and in the authors’ reporting of outcomes, and a lack of detailed statistical information in many studies, precluded a meta-analysis. Therefore, the authors adopted a systematic narrative approach to report the study’s key findings.

First, we conducted a search to identify existing studies on implemented Tier 1 interventions targeting caregiver–child interaction quality or caregiver-child interaction quality and children’s socio-emotional development. Specifically, we were interested in intervention studies whose outcomes were the quality of caregiver–child interaction and/or the socio-emotional development of the child, not only children’s cognitive school readiness. For this reason, the following inclusion criteria were adopted: (a) articles published between January 2007, when the ECEC Network was established, and July 2021; (b) empirical studies in peer-reviewed, English-language scientific journals; (c) studies with samples comprising teachers/childcare providers (center-based, home-based, and preschool) of children aged 0–5 years; (d) Tier 1 intervention studies focusing on caregiver–child interaction quality or caregiver–child interaction and children socio-emotional development. Moreover, these interventions should have been (e) implemented and (f) include caregiver–child interaction quality and/or children socio-emotional development as outcome variables.

We excluded: (a) intervention studies with samples comprising teachers/childcare providers of children aged >5 years; (b) non implemented and empirical evaluated studies; (c) Tier 2 and Tier 3 studies (focus on at-risk children with behavioral problems) and in general samples including children with developmental issues; (d) grey literature; (e) articles whose full-text could not be accessed.

Detailed information was drawn from each of the relevant articles using a researcher-developed data extraction sheet. The following areas were included: (1) authors, year of publication, and country of data collection; (2) information on the implemented program (name of the program, if it has been validated or not/or if it has been adapted from other validated programs); (3) school characteristics: type of school and type of childcare (center-based childcare or home-base childcare); (4) sample characteristics: number of schools/centers enrolled, number of classes, teachers/caregivers information (number of teachers/caregivers enrolled, gender, average age, education level, years of experience), children information (number of children enrolled, average number of children per classroom, gender, age, SES background, and teacher/child ratio (number of children per teacher) during the intervention implementation; (5) intervention characteristics: TTI dimensions of the teacher–child interaction targeted by the intervention (ES, CO, IS), in-person/web-based intervention, if the intervention includes a group and/or an individual training, activities and duration of training, usage of video and type of video training used (video-modeling or video-feedback), if the intervention included follow-up activities after the intervention, a children curriculum, and a control group; (6) measured variables: outcome variables (evaluated with structured observation or with self-report questionnaires), predictors or covariates, moderators, acceptability/satisfaction/usefulness of the program reported by participants, agreement between teachers and experts evaluations; (7) main results.

3. Discussion

Among structural features of professional care, the child–caregiver ratio is generally considered the most important, especially for infants and toddlers [42,43]^[17][18]. The greatest part of the studies included in our review specified teacher/child ratio during the implementation of the intervention. Data revealed that the caregiver-child ratio [4]^[5] and time spent with trusted caregivers [5]^[1] are related to the outcomes of interventions designed to strengthen teacher–child interactions in ECEC. In the past decades, other studies consistent with these results recognized with broad consensus that the size of the group of children is associated with more sensitive, responsive, and warm professional caregivers’ attitudes [44,45,46]^[19][20][21]. Dimensions of educator–child interaction and children’s wellbeing could benefit from reexamining the actual caregiver–child ratio in ordinary care. In order to obtain greater insight into this theme, experimental manipulation of the child–caregiver ratio in early education contexts is needed [47]^[22].

Several studies, indeed, showed that teachers with more experience and higher education are better at regulating their emotions, being responsive to children’s needs, and encouraging children in expressing themselves in the classroom, when compared to teachers with less experience and education [51,52,53,54,55]^{[23][24][25][26][27]}. Far from meaning that more experienced or educated teachers directly lead to better child development (e.g., see [56]^[28]), such studies suggest that teachers’ characteristics may have a main role in promoting children’s social and emotional skills. It is likely, indeed, that teacher characteristics’ play a role in a wider system of factors (e.g., children features, school features, social, and cultural conditions) influencing the teacher–child interaction, as well as children’s emotional and social development [57]^[29].

The reviewed studies underlined that effective implementation (minutes on website/if teachers implemented at least one session of the intervention with children [23]^[30]) and the topic of the intervention training [28]^[31] (if it is more focused on emotional support rather than on classroom organization only) are related to the results of the interventions.

Considering the topic of studied interventions, in terms of TTI teacher–child interaction dimensions that programs targeted, the majority of them were focused on the ES dimension, and only five of them targeted all the three dimensions together (ES, CO, and IS). According to Downer and colleagues [23]^[30] it is important not to conceptualize the TTI system in a purely aligned way, examining ES in relation to socioemotional development, CO with self-regulation skills, and IS with academic and cognitive outcomes only [18]^[15]. Cross-domain relationships should be taken into account to better understand the bidirectional influence between teachers and children [18]^[15]. Future intervention studies designed to enhance socioemotional development in children will benefit from the inclusion of not only of the ES dimension but also of CO and IS practices.