The study attempted to assess student learning and retention in physics following various types of help sessions based on objective-referenced diagnostic tests. Students from an undergraduate physical science course were assigned to one of four treatment groups or a control group. The four treatments consisted of help sessions, each with a different degree of instruction using a list of objectives for each exercise studied in the laboratory and a diagnostic test based on the objectives. At the conclusion of the three-week study a criterion test of physical science laboratory achievement was administered to all students and a similar test of a comprehensive nature was administered six weeks later as a retention test. Results from this study confirm the value of diagnostic tests. All students taking diagnostic tests performed better than the control group students on both criterion tests. (Author/MH)