Teacher ratings of 336 preschool children (mean age = 48 months) attending two urban Head Start programs were collected to examine the influence of contextual variables of teacher training, classroom, and site on the prevalence of significant problems. The prevalence of externalizing behaviors in the "problem range" was higher than expected and fewer children were rated in the "well-adjusted range" on social competence measures. Psychometric characteristics of the ratings indicated that teachers in this urban setting were less consistent in their ratings of internalizing problems, calling into question the lack of elevation of such problems in this population. Ratings by teachers and teacher assistants of the same children showed low agreement; the level of ratings was not affected by differences in training but did vary across classrooms. Hierarchical linear modeling analyses of the entire sample showed significant effects of classroom and site on problem behaviors and social competence. These results reveal the wide variation in problem frequency across classrooms, which needs to be considered in the implementation and evaluation of evidence-based interventions. Further, these results point to the importance of studying possible lasting effects on children exposed to these differing contexts.