Randall I. Charles, Frank K. Lester, Jr., An Evaluation of a Process-Oriented Instructional Program in Mathematical Problem Solving in Grades 5 and 7, Journal for Research in Mathematics Education, Vol. 15, No. 1 (Jan., 1984), pp. 15-34
No takes yet. Share an insight, caveat, or question.
Charles et al. (1984) studied this question.