Globally, children are legally obliged to attend school at a certain age (ranging from 4 to 7 years old). Developmental differences are rarely considered at school entry nor are they always reflected in the teaching and learning environment. Children who start school without being ready to cope may be significantly disadvantaged. Failure at school can impact directly on long-term outcomes such as unemployment, crime, adolescent pregnancy, and psychological and physical morbidity in adulthood. In contrast, experiencing success at school can impact positively on a child's self esteem, behaviour, attitude, and future outcomes. School readiness interventions aim to prepare a child for the academic content of education and the psychosocial competencies considered important for learning such as self-regulation, listening, following instructions and learning to share in play and other social settings. There is a need for evidence of the effectiveness of centre-based school readiness interventions. To evaluate the effectiveness of centre-based interventions for improving school readiness in preschool children. In October 2021 we searched CENTRAL, MEDLINE, Embase, ERIC, PsycINFO, ERIC, eight additional databases and three trials registers. Other eligible studies were identified through handsearches of reference lists, reports, reviews and relevant websites. We included randomised controlled trials (RCTs) and quasi-RCTs comparing centre-based school readiness interventions to no intervention, wait-list control or treatment as usual (TAU) for children (aged three to 7 years before starting compulsory education). The primary outcomes were school readiness and adverse effects. We used standard methodological procedures expected by Cochrane. We used GRADE to assess the certainty of evidence. We included data from 32 trials involving 16,899 children (6590 included in at least one meta-analysis). Four studies compared centre-based early education interventions with no treatment controls. Twenty-two trials compared an enriched school curriculum to treatment as usual (TAU). Children were aged between 3 and 7 years old (mean age 4.4 years), 51.7% were boys and at least 70% were from a racial/ethnic minority group. Most studies were conducted in the USA and mainly located in areas of high socioeconomic deprivation. Interventions were delivered in centre-based settings (pre-kindergarten or elementary schools), for at least one half day, 4 days per week over the academic year. Follow-up ranged from up to 1 year (short-term), 1-2 years (medium-term) and over 2 years (long-term). We judged the certainty of evidence to be very low to moderate across all outcome measures. We downgraded the certainty of the evidence because the included studies were at an unclear or high risk of bias due to poor reporting, imprecision arising from small sample sizes and wide confidence intervals, and inconsistency due to statistical heterogeneity. Most studies were considered to be low or unclear risk for selection, detection, performance, attrition, selective reporting, and other bias. Allocation bias was at high risk in 10 studies. The US federal government funded most of the studies. Comparison 1. Centre-based early education interventions for improving school readiness versus no interventionCognitive development. There may be little to no difference in cognitive development between centre-based early education interventions and no intervention at long-term follow-up (MD: 3.28, 95% CI: 0.23 to 6.34; p = 0.04; 2 studies, 361 participants; low certainty evidence). Emotional well-being and social competence. There may be no clear difference in social skills in centre-based early education interventions compared to the no intervention control group at short-term follow-up (SMD: -0.11, 95% CI: -0.54 to 0.33; p = 0.63; 3 studies, 632 participants; low certainty evidence). Heterogeneity for this outcome was substantial (I² = 71%). Health development. Narrative analysis from a single study showed that centre-based early education interventions may improve health development outcomes such as health checks, immunisation compliance and dental care (1 study, 142 participants; low certainty evidence).None of the studies reported on school readiness, adverse effects, or physical development. Comparison 2. Centre-based early education interventions for improving school readiness versus TAUSchool readiness. The evidence is very uncertain about the effect of centre-based early education interventions compared to TAU on school readiness up to 1 year post-intervention (SMD: 1.17, 95% CI: -0.61 to 2.95; p = 0.20; 2 studies, 374 participants; very low certainty evidence). Heterogeneity for this outcome was considerable (I² = 95%). Cognitive development. The evidence is very uncertain about the effect on cognitive development between centre-based early education interventions and TAU at long-term follow-up (MD: 9.34, 95% CI: -6.64 to 25.32; p = 0.25; 2 studies, 136 participants; very low certainty evidence). Heterogeneity for this outcome was considerable (I² = 92%). Emotional well-being and social competence. A meta-analysis of 12 studies demonstrated there may be little to no difference in social skills between centre-based early education interventions and TAU at short-term follow-up (SMD: 0.11, 95% CI: -0.05 to 0.28; p = 0.19; 12 studies, 4806 participants; low certainty evidence). Physical development. Evidence from one study showed that centre-based early education interventions likely have little to no difference in increasing fine motor skills compared to TAU at short-term follow-up (MD: 0.80, 95% CI: -1.11 to 2.71; 1 study, 334 participants; moderate certainty evidence).None of the studies measured adverse effects or health development. We found very low, low and moderate-certainty evidence that centre-based interventions convey little to no difference to children starting school compared to no intervention or TAU, up to 1 year. More research, measuring relevant outcomes, conducted outside the USA, is required to improve programmes designed to meet the needs of children starting school.