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Early childhood is a critical period for cognitive development, yet substantial developmental disparities persist despite global policy efforts. To address these inequalities, large-scale early childhood interventions have increasingly been integrated into public systems and policies. However, scaling introduces challenges related to variation in context, coverage, and implementation fidelity, raising questions about real-world effectiveness. Existing reviews have primarily focused on small-scale or targeted interventions, leaving a limited synthesis of evidence on population-level approaches. This study systematically reviews evidence on scaled early childhood interventions aimed at enhancing cognitive development in children aged 0–8, analyzing their design characteristics, implementation processes, outcome measures, evaluation methodologies, and overall effectiveness.
Methods
A comprehensive literature search was conducted across ten electronic databases: APA PsycInfo, Applied Social Sciences Index & Abstracts, ERIC, Education Database (ProQuest), British Education Index, EconLit, Education Full Text (H.W. Wilson), Family & Society Studies Worldwide, Global Health (EBSCOhost), and Web of Science, covering studies published between January 1, 2010, and March 31, 2025. Studies were eligible if they evaluated scaled interventions targeting children aged 0–8 and/or their families, employed experimental or quasi-experimental designs, and reported at least one cognitive development outcome. Interventions were considered scaled when implemented beyond a single pilot or efficacy trial, reflecting real-world delivery. Following deduplication of 6,924 database records, 5,272 references were screened, 270 assessed for full-text eligibility, and 75 met all inclusion criteria; additional studies from citation searching and grey literature yielded a final sample of 79 studies. Data were extracted on intervention characteristics, implementation features, outcome measures, evaluation approaches, effectiveness indicators, and costs where available.
Results
The 79 included studies spanned 33 countries, yet nearly half originated from high-income countries (HIC, n=38), with the United States alone accounting for 28% of the evidence (n=22), and low-income countries were markedly underrepresented (LIC, n=6). Parent-focused was the most common type of scaled intervention, followed closely by child-focused education, teacher/curriculum interventions, and comprehensive/multisectoral interventions. Intervention type varied notably by income context: teacher and curriculum-focused interventions predominated in HICs, while comprehensive multisectoral approaches were more common in LMICs and LICs. Interventions operated most commonly through education systems and community-based platforms. Fidelity monitoring was absent in 23 studies, and cost data were reported in only 17. Preliminary synthesis of effect sizes from RCT studies suggests that most studies found small but statistically significant effects on cognitive development, though a substantial proportion of estimates were not statistically significant.
Conclusions and Implications
The study demonstrates that evidence for scaled early childhood interventions predominantly originates from high-income countries, reflecting implementation-evaluation gaps rather than an absence of large-scale programs in low-income contexts. Intervention models systematically vary by national income levels, with resource availability shaping design and scaling strategies. Pervasive gaps in fidelity monitoring and cost reporting limit the ability to draw robust conclusions about real-world scalability. To address these limitations, we recommend equity-focused research funding, standardized implementation metrics, and meta-analyses to examine heterogeneity across intervention types, delivery mechanisms, and target populations.