This paper examines the relationship between quality of instruction of faculty members as assessed by students and the assessment periods involved. It is based on analysis carried out in Israel's largest public college. Our aim was to explore whether investments to improve the quality of instruction of faculty members are cost beneficial. The findings of this study confirm an improvement in all faculty members' ratings on assessment items as measured in instruction assessment surveys conducted at four points in time. Yet, the findings also indicate that improvements in teaching were not related to instructors' participation in teaching workshops or to any other steps taken by the college to improve quality of teaching. On the whole instructor's age was found to be an individual attribute variable of paramount importance. Seniority turned out to be another important professional attribute variable. (Contains 19 tables.)