Sample Size
The sample size was calculated based on the primary outcome and a noninferiority margin of −3.3 points. Based on the historical data obtained from the schools before the trial, the median academic score distribution was level B (≥75 to <85 points). Therefore, a decrease of 10 points was expected to change the final mathematics performance from level B to C. The noninferiority margin (the level at which the intervention was noninferior to the control) was chosen as one-third of the range of 10 points. The sample size estimation was conducted based on the assumption of a 1-sided α = .025, 90% power, an intraclass correlation of 0.10, an SD of 7 for mathematics scores, a mean cluster size of 60 children (2 classes per cluster with a class size of 30), and less than 5% of children being lost to follow-up. The sample size required was 12 schools per group or a total sample size of 24 schools. The PASS software, version 16.0 (NCSS) was used for the calculation.