Three Chinese children with mental retardation were trained single-digit addition without carrying (or regrouping) using the microcomputer. The major objective was to foster an automatic and accurate response in these children when they were presented with simple addition problems. The training program incorporated a number of behavioral instruction techniques including demonstration, repetitive practice, corrective feedback, and token reinforcement. The instruction was conducted through a personal computer. To evaluate the training effect, a multiple-baseline across subjects design with followup was employed. Results showed that the children's response latency and accuracy in single-digit addition improved with training and their performances were maintained at 12th week following training. Generalization data showed a direct transfer from the computer to a paper-and-pencil task. When the additions were presented in a horizontal rather than vertical form, children had to be prompted before transfer took place.