Students' evaluations of teaching effectiveness (SETEs) are weakly related -- negatively -- to teaching experience and age according to Feldman's (1983) comprehensive review of cross-sectional studies. These studies, however, provide a weak basis for inferring the future ratings of less experienced teachers or the past ratings of more experienced teachers. Considered here are ratings of 6024 classes taught by a diverse cohort of 195 teachers representing 31 academic departments who were evaluated continuously over a 13-year period using the same multidimensional SEEQ instrument. For both undergraduate and graduate level courses, there was almost no linear or nonlinear changes over time for any of the 9 content- specific dimensions, the overall course rating, or the overall instructor rating. The findings were consistent for teachers who had little, moderate, or substantial amounts of teaching experience at the start of the study. These results are important because this is apparently the only study to examine this issue using a longitudinal design with a large and diverse group of teachers over such a long period of time.