The research project "Feedback Processes in Computer Managed Spelling Instruction" is aimed at developing and testing an instructional software program for teaching the orthography of Dutch verbs. The main focus of this paper is on how to design an optimal educational environment. The design of the man-computer interaction is highlighted from a number of aspects: the sequencing of the learning content, the presentation of information on the screen, and the format of student input and feedback. The program consists of seven instructional modules, each focusing on a grammatical operation such as grammatical tense, person, number and voice. Two versions of the program, a Standard Version and a Flexible Version, were field tested and the results were compared, taking account of individual differences in spelling ability and motivation variables. Results indicated that no strong interactions between treatment variables and student characteristics could be established; however, on the whole, the software proved to be effective. (6 references) (Author/DB)