This study explores a learning model which suggests that a concept is acquired first through manipulation of concrete objects followed by transformation of the concrete objects into semi-concrete representations, followed by internalization of the concept through abstract representations. Microcomputer simulations of manipulative activities were used to determine how children differ in their use of science-process skills and concepts when using the simulations compared to using the concrete materials, or a combination of simulations and concrete materials. Subjects included 113 children distributed according to male and female, second- and fourth-grade level, and socio-cultural site. Criterion measures assessed the children's ability to: recognize and duplicate a design; recognize and extend a pattern; and locate objects in space. Results indicate that: (1) fourth graders performed better than second graders; (2) rural, white children performed better than suburban, black children with activities involving the computer; (3) rural, white girls performed better than suburban, black girls using concrete-only activities; and (4) rural, white boys using activities involving the computer performed better than suburban, black girls using concrete-only activities. These findings suggest that concrete and computer activities have different effects on children depending upon their socio-cultural background and upon their sex. (Author/JN)