A study involving 338 students in six different lower-division physics courses is reported in which students' Piagetian levels of intellectual development as determined by a written questionnaire versus final semester grades are compared. A good correlation would provide the instructor with a useful counseling tool while a poor or zero correlation would not. In either case, the questionnaire results can guide the selection of instructional materials and techniques for the class. The correlation coefficients were found to be positive, but low, for the grades A, B, and C, and the statistical scatter diagrams show a wide spread of Piagetian levels of intellectual development within each letter grade level. Other factors than the ability to think logically appear to be of greater importance for the D group, and no correlation can be seen for the W's and F's. The wide spread of Piagetian levels of thought for each grade level suggests that students can somehow attain passing, if not high, grades in the more elementary of these courses even though they appear to lack the ability to think formally, at least at the beginning of the course. Logical thought appears to be a more necessary attribute as students progress through the engineering physics sequence, however.