This study investigated whether classroom quality is related to child progress in meeting developmental milestones. The study used the "Assessment Profile for Early Childhood Programs: Research Version," a developmental checklist administered by teachers in a Head Start program. Findings indicated that pre-assessment and child age account for the majority of variability in child post-assessment scores, suggesting that teachers have a somewhat limited ability to influence child progress toward developmental milestones as measured by this type of assessment. The pre-assessment slope model suggests that factors beyond the pre-assessment alone are more likely to influence the developmental trajectory of children in smaller classrooms and those with younger children. Findings also indicated that a teacher who is able to tailor classroom activities to the unique needs of younger children may be more likely to facilitate those children's development toward the class average score. While the magnitude of the effect is small, these results show that high quality teachers can impact even the developmental trajectory of a child by recognizing individual needs. (JPB)