We selected the inclusion criteria to ensure that any selected school in the sample would have a majority of racial or ethnic minorities. We randomly selected the sample sites in a proportional-to-size random sample clustered by age group except for the Head Start preschools, for which we used simple random sampling. As the study progressed,we added several schools that met the above criteria to increase the representation of Asian and Black children. Our sample goal was to recruit 50 students from 45 sites (15 sites for each age group) for a total of 2250 children.