You are interested in how teacher feedback on homework (e.g., "good going" or "m

(1) Laboratory experiments require tight control. Students would be randomly assigned to an experimental group (comments) or a control group (no comments). Comments would be systematically given to the first group over time. The second group would complete identical assignments, but not receive comments. The assignments of both groups would be evaluated. (2) Single case experiments would involve one group of students. No comments on homework would be given. Results would be evaluated. Then, comments would be introduced and analyzed. (3) A randomized field experiment would involve two classes. The design would be the same as for the laboratory experiment, but methods would be more natural and less controlled.