In early computer assisted instruction (CAI), negative feedback often insulted students and/or provided no useful knowledge. In classroom settings, teachers use the following approaches in dealing with students' wrong answers: (1) ask the question again, louder and slower; (2) ask the question again, using different words; (3) back up and reteach the past three minutes/hours/days; and (4) keep still, listen to the students and let their behavior reveal where the source of the misunderstanding lies. The latter approach suggests that students answer correctly or incorrectly for a reason and that observation of their behavior can indicate ways to help them correct their misunderstandings. For example, using algorithms to describe student behavior can help minimize student errors in learning a procedure. Designing CAI materials for procedural learning should include two steps: construction of the correct production system or algorithm and construction of potential "buggy" or incorrect procedures, followed by incorporation of instructional error checking into the program. This paper concludes with the description of an interactive video program developed to teach procedures for diagnosing reading problems which included three incorrect algorithms. Responses to students' choice of incorrect algorithms were positively phrased and offered hints. Responses for correct answers explained why the answer was correct. Three references are listed. (LMM)