Graziano & Raulin
Research Methods (9th edition)
Non-Equivalent Control Group Question #1
This is a complicated question that depends on a lot of variables, some of which may not be immediately obvious.
For example, if the course is one that is taken by a large number of freshman, there is a large difference between freshman in the fall and spring semesters. Many freshman are not ready for college. They fail to study during the first semester and do poorly. Some drop out or are put on probation. Others realize that they have to work harder if they want to avoid failing and therefore study harder in the second semester. This effect is rather large for freshman, but negligible for juniors and seniors.
The time of day that the class is taught influences who will take the class. If the class is taught at 11:00 AM one semester and 8:00 AM the next semester, it is entirely possible that the mix of students will be different in those two classes.
Finally, performance on the exam is a function of both the clarity of the textbook and the performance of the teacher. Therefore, it is critical that the teacher use the same approach in each semester, which may be difficult because some of the instructor's coverage will be dictated by what is covered in the text.