A study of the effectiveness of formative evaluation and remediation activities in achievement of intellectual skills was made, involving a general science teacher and his four classes of 90 eighth grade students. Subjects were ranked by using the Arithmetic Skill Test of the Iowa Tests of Basic Skills and randomly assigned into three treatment groups. Each group was further divided into seven levels of the classification variable. All subjects were first presented a tape-slide instructional program and then took a diagnostic test. The remedial activity materials were delivered in the following day. Group 1 received an alternative form of instruction designed to teach similar objectives, while group 2 received additional practice items. No additional instruction was given to group 3. A 13-item measuring instrument was used. Analyses showed that, in remediation of learning errors, the alternative form of instruction was proved more effective than the use of additional practice items, agreeing with Gagne's hypothesis. Group 1 and group 2 achieved better than did group 3. Diagnostic tests were proved important in the production of higher student performance. Implications for classroom teachers and curriculum designers are provided. (CC)