This study reports the results of a field-based investigation of the effects of two motor intervention approaches-neurodevelopmental treatment and developmental skills-on children with two different diagnoses. The sample included 50 children, of whom 27 were diagnosed as having Down syndrome and 23 as having cerebral palsy. Children had a mean chronological age of 14 months at the beginning of the study. The severity of their motor impairment was assessed with the Gross Motor Function Classification System for Cerebral Palsy. Children's motor functioning was examined at entry into the study and after they received 1 year of motor intervention services. Dependent measures included children's general development, rate of motor development, and quality of movement. Pre-post comparisons indicated that children made significant changes in their motor development age and quality of movement over the course of intervention. However, there was no evidence that motor intervention accelerated development or improved quality of movement beyond what could be expected on the basis of maturation. Furthermore, no differential intervention effects were associated either with children's diagnosis or treatment model. Regression analyses indicated that the rate of motor development children attained after 1 year of intervention was highly related to their rate of development at the onset of intervention and, to a lesser degree, to the number of sessions of intervention children received. These results are discussed in terms of the need for the field of motor intervention to develop new treatment paradigms.