Background: This study tested a preschool-home partnership intervention, in which early childhood teachers encouraged the parents/caregivers of preschoolers to engage in dialogic reading at home. This was an experimental test of Bronfenbrenner's hypothesis that parental involvement in early care and education programs should promote child development, as well as a test of a train-the-trainer approach to the dialogic reading intervention. Objective: The current study focuses on testing the causality of parent involvement: (1) homework assigned to parents/caregivers will improve the early language and literacy skills of their 2 ~ 3-year-old children; (2) gains by children in the intervention group with low pre-test language and literacy score, low family literacy score, and high parents/caregivers' extent of using dialogic reading strategies at home will show larger gains in literacy scores than their counterparts. Methods: A sample of 12 early care and education programs, 18 early childhood teachers, 87 two--to three-year-old children and their parents/caregivers were followed for 18 ~ 20 weeks after assignment to the intervention group or the control group. Results: The impacts of the six-week parent involvement intervention continued to grow during the six-week follow-up phase, and represented substantial gains of the intervention group in four aspects of early language and literacy skills. Conclusion: This study provides evidence that a simple homework assignment intervention can be an effective tool to promote child development when parents/caregivers are engaged. The intervention also had ongoing influence on children's early language and literacy skills, even after the intervention period had ended.