A study was made between matched pairs of students from two separate years. One year the students were assigned problems but no check-up was made as to whether the problems were solved. The next year the same textbook and lessons were used, but the students were required to hand in six solved problems three times per week. The criterion of success was the scores made on the Coöperative Physics Test. Approximately 130 matched pairs of students were studied consisting of various levels of ability
