A growing debate exists over the possibility that various types of external rewards may have negative effects on intrinsic motivation. Past research has produced conflicting results. The present study examines past research in light of behavioral principles and utilizes single-subject research methods to examine the potential effects of ability--and effort-based verbal praise statements on mathematics task performance and task persistence. Results of this study do not support the criticism uniformly leveled against external rewards generally or ability-based praise specifically. Limitations and directions for future research are discussed.