This study was designed to examine the effect of different kinds of adult mediation on the cognitive performance of young children who used computers. The study sample included 150 kindergarten children aged 5-6. The findings indicate that children who engaged in adult-mediated computer activity improved the level of their cognitive performance on measures of abstract thinking, planning ability, vocabulary, and visual-motor coordination, as well as on measures of response style including reflectivity. Their performance on these measures was better than that of children engaged in computer activities without adult mediation or with very little mediation (accompaniment). Based on the findings, it may be concluded that integrating teacher mediation within computer learning environments for young children facilitates informed use of computer technologies in their learning system, and enhances thinking processes and work habits.