Active Start: Physical Activity for Children Birth to Five (2002), proposes that preschoolers should develop competence in fundamental motor skills prior to starting school since these skills are the building blocks for more complex movement tasks. The purpose of this study was to determine the effectiveness of a mastery climate motor skill intervention on young children’s locomotor and object control motor skill development. Thirty-six, 3-year-old participants were assigned to one of two groups, intervention or comparison. The intervention group (n = 8) was exposed to a 15-week motor skill program that met for 30 minutes per session 2 times per week, that incorporated a mastery motivational climate proposed by Ames (1992). The comparison group (n = 28) did not participate in the program. Prior to and following the intervention period, participants were asked to complete the Test of Gross Motor Development-II (TGMD). The TGMD is a 12-item assessment comprised of two subscales: locomotor skills and object control skills. Separate 2 x 2 ANOVAs (Group x Time) with repeated measures on the last factor were conducted to determine the effectiveness of the motor skill intervention on the locomotor and object control subscales of the TGMD. The analyses revealed a significant Group x Time interaction for the locomotor, F(1,34) = 6.80, p < .01, h2 = .17, and object control subscales, F(1,34) = 24.42, p < .001, h2 = .42. Follow-up analyses showed that the intervention group significantly improved in locomotor and object control performance from the beginning of the program to the end, while the comparison group failed to demonstrate significant change. The follow-up analyses for the locomotor subscale indicated that the intervention group performed significantly better than the comparison group prior to and following the intervention. For the object control subscale, the follow-up analyses showed that the groups did not differ significantly prior to the intervention, however, the group who received the intervention did perform significantly better than the comparison group after the 15-week period. These findings suggest that the mastery climate motor skill intervention had a dramatic influence on the participants’ motor skill development, while the results of the comparison group suggest that young children need intervention to improve their fundamental motor skills. These findings support the need for effective intervention for young children in order to meet the objectives of the Active Start guidelines.Keyword(s): community-based programs, early childhood, research