The belief that intelligence is malleable has important consequences for achievement and motivation (Blackwell et al. "Child Development," v78, p246-263. 2007; Dweck, 1999; Robins & Pals, "Self and Identity," v1, p313-336, 2002). However, believing that it is possible to improve intelligence does not necessarily mean students are always confident they can improve their own. The current study presents a revised "self-theory" measure of the implicit theories of intelligence scale, which assess students' beliefs about their ability to mold their own intelligence in contrast to their beliefs about the malleability of intelligence in general. In testing with 643 Australian high school students (62% female) ranging from 15 to 19 years of age (M?=?16.6, standard deviation (SD)?=?1.01), the belief that intelligence is "fixed" was predictive of lower endorsement of achievement goals, greater helplessness attributions, and poorer self-reported academic grades. Fixed "entity" beliefs were also predictive of academic self-handicapping, truancy, and disengagement. On all of these measures, the new self-theory scale uniquely explained greater outcome variance. These results indicate that students' implicit beliefs--particularly about their own intelligence--may have important implications for their motivation, engagement, and performance in school.