in non-collegial work settings (Rosenholtz, 1986). A possible cause of this curvilinear trend in experience effects is that older teachers do not always continue to grow and learn and may grow tired in their jobs. Furthermore, the benefits of experience may interact with educational opportunities. Veteran teachers in settings that emphasize continual learning and collaboration continue to improve their performance (Rosenholtz, 1984). Similarly, very well-prepared beginning teachers can be highly effective. For example, some recent studies of 5-year teacher education programs— programs that include a bachelor’s degree in the discipline and master’s in education as well as a year-long student teaching placement—have found graduates to be more confident than graduates of 4-year programs and as effective as more senior teachers (Andrew & Schwab, 1995; Denton & Peters, 1988).
It is also possible that uneven effects of experience in cross-sectional studies can be the result of cohort effects (for example, cohorts of teachers hired in times of shortage may be less well-qualified than those hired when schools can be more selective) or of attrition effects (for example, disproportionate early attrition of more able teachers may leave a less capable senior force on average) (Murnane & Phillips, 1981; Vance & Schlechty, 1982). Presumably, the direction of this effect would change if retention policies kept the most able beginning teachers in the profession. Since experience is also correlated with teacher education and certification status, these variables may be confounded in some analyses.