The study was to compare the effects of modeling, verbal instruction and modeling plus verbal instruction on motor skill development and cognitive acqusition among mental retarded children. Seventy-two subjects from three age levels with mean IQ of 57.74 and CA of 9.72 years were obtained. A 3(grades)×3(types of experimental treatment)×4(trials)repeated measures design was used. The subjects´ performance on the two tasks involving putting electric wires in a plug with a screwdrive and assembing a rabbit picture was examined. The results were as followed. (1) Modeling plus verbal instruction proved to be significantly more effective than the other two. (2)There was a significant effect of trials on the performance of the two tasks. (3)No significant difference in cognitive acquisition was found among the three age levels, but there was a significant difference in motor skill performance between the first and the third age levels.