ABSTRACT.The effectiveness of computerized handwriting instruction incorporating modelling of the target letter, corrective feedback and reinforcement contingent upon letter accuracy was examined with severely mentally retarded adults. Assisted by faded prompts on a sheet of paper, subjects wrote the letter ‘q’ while their handwriting patterns were detected by a digitized graphics tablet linked to a computer. Computerized instruction was introduced for six subjects (mean mental age = 3 years, 10 months) according to a multiple‐basetine‐across‐subjects design. Instruction produced significant improvements in letter quality which were not simply due to the effects of practice. Subjects who had extended practice before being introduced to the computer were less responsive to the information provided by the computer and did not attain the levels of performance accuracy achieved by other