Two studies examined the effects of social-comparison versus mastery praise on 4th- and 5th-grade children’s intrinsic motivation. Children received a high score and either social-comparison praise, mastery praise, or no praise for working on a set of novel puzzles. They then worked on a different task and were given either ambiguous feedback (Study 1) or positive feedback (Study 2) before completing measures of intrinsic motivation. Mastery praise enhanced intrinsic motivation and social-comparison praise curtailed it when uncertainty about children’s subsequent performance was introduced (Study 1) and, for girls, even in situations of continued success (Study 2). Social-comparison praise also tended to discourage children from seeking subsequent self-evaluative normative information. Theoretical and practical implications are discussed.