This study tests the effectiveness of 2 approaches to parenting instruction for parents of preschool developmentally delayed children aged 3 through 5. Sixty parent/child pairs were randomly assigned to 1 of 3 groups: (1) individual parenting instruction only, (2) individual plus group instruction, and (3) comparison group with no instruction. Parent instruction programs were individually designed to teach parents to change their interactions with their child, decrease areas of conflict, and increase self-esteem of both parent and child. Pre- and post-treatment assessment included direct observation of play sessions and administration of a battery of standardized tests. Pre-tests showed no significant differences between the 3 groups. Post-tests indicated that there were changes in both parents and children. Final assessment after 1 year indicated that the treatment groups were clearly different from the comparison group and individual instruction appeared to be both economical and effective. While interactional changes occurred, overall child developmental levels and parent appraisals of their children's developmental delays remained the same. Children in treatment groups made large positive gains in social interaction. Results suggest that high negative affect between mothers and developmentally delayed children can be changed. (Author/RH)