This study compares the effects of relationship-focused early intervention on toddlers and preschool-age children who were classified as having either pervasive developmental disorders (PDDs) (N = 20) or developmental disabilities (DDs) (N = 30). The intervention was conducted over a 1-year period through weekly individual parent-child sessions. It focused on helping parents use responsive teaching strategies to encourage their children to acquire and use pivotal developmental behaviors that addressed their individualized developmental needs. Before and after comparisons indicated significant increases in parents' responsiveness and children's pivotal behavior. Both groups of children made significant improvements in their cognitive, communication, and socioemotional functioning. However, children with PDDs made statistically greater improvements on the developmental measures than children with DDs. On several developmental measures, children's improvements were related to increases in both their parents' responsiveness and their own pivotal behavior.