The individual growth trajectories were fitted in the level-1 model. Each child’s outcome scores were modeled as a function of time. First, the unconditional curvilinear growth models were tested by adding a quadratic term for time to the level-1 model, and the Deviance Tests indicated that the outcomes changed over time with a significant quadratic pattern. For teacher outcomes, the data collection dates at each wave were very close in time. Therefore, the time variable for teacher outcomes is 0 as baseline, 1 as post-intervention, and 2 as 1-year-follow up. For parent outcomes, the data collected with each wave were spread across several months, so we took the actual time interval from baseline as the time variable, setting baseline to zero. Each of the growth parameters in level-1 model has a substantive meaning and was estimated in level-1 model. The intercept was set as initial status at baseline. Time slope was the linear change rate over time, and the quadratic term represented the curvilinear change across time, capturing the curvature or acceleration in each growth trajectory.
