Although the topic of stability and change in classroom impressions research is not new, there remain unanswered questions about what impressions are stable, when they are likely to change, and for whom they are likely to change over the course of a semester. My research will begin to answer those questions. My research took place in four college classroom studies and assessed students' impressions of their instructor's teaching effectiveness and personal qualities 1) after the first day of class, 2) before and following at least one exam, and 3) at the end of the semester. My results supported previous findings that early and later impressions are stable (i.e., significantly and positively correlated) (Studies 2, 3, and 4). Ratings of teaching effectiveness and personality changed (Studies 3 and 4), with teaching effectiveness ratings changing more than ratings of personality (Study 4). I split students based on low versus high exam performance (bottom third and top third of scores, respectively), as performance was expected to relate to how students rated their instructor. Initial ratings did not differ based on future performance, suggesting no preexisting differences between the groups. However, ratings of the instructor's effectiveness and personal qualities changed following the first day (Studies 3 and 4). In Study 3, both types of ratings improved; high performers rated the instructor as significantly more effective than low performers. The two groups did not consistently differ in ratings of personal qualities. In Study 4, ratings on both measures worsened following receiving the first exam feedback and high performers' ratings were significantly higher than low performers' ratings following the initial impression. My research offers evidence that actual students' judgments of their college instructor are based on their accumulating experiences in the classroom, not on the first impression alone. This is encouraging news to instructors worried about their first impressions. It is also a warning to instructors who think that they can coast following a good first day of class. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]