In this experimental study, music teachers from a large school district were randomly assigned to one of two hypothetical conditions reflecting different methods for measuring student growth under a merit pay compensation system. In Scenario A, half of a teacher's effectiveness rating was based on student standardized test scores in reading, writing, and math. In Scenario B a portfolio of student work and musical performances was used to determine teacher effectiveness. Participants responded to statements concerning how their motivation, instructional practices, school climate, and career commitment would be affected if they were working under merit-pay conditions described in the scenario. Results indicated that the portfolio-based approach to measuring music teacher effectiveness yielded higher levels of music teacher motivation and career commitment than one based on standardized test scores. Additionally, music teachers not enrolled in a merit-pay program reported a significantly higher level of career commitment when assigned to the portfolio-based scenario.