At level-2, the person level, the child characteristics (gender and genotype (with genotype grouped into A/A and carriers of the G allele)) were entered as control variables in the intercept, and child characteristic (gender and genotype and the interaction terms genotype by gender) was examined as a potential moderator of the child’s rate of change and effect of intervention on behavior outcomes over time at level-1 model. Child characteristics were group mean centered. The intercept and time slope were treated as random effects at level-2. The quadratic term was treated as a fixed effect for teacher outcomes with three times of measurements, and as a random effect for parent outcomes at level-2 because of four times of measurement.
