In this paper we report the results from a study that assessed confidence together with scales measuring self-belief--i.e., self-efficacy, different kinds of self-concepts, and anxiety--among the 15-year old students from Singapore. A distinct confidence factor was identified in the domains of mathematics (N = 1940) and English (N = 1786). Our results show that confidence is: a) a robust individual differences dimension; b) that can be combined with accuracy information to obtain bias scores that may be useful for group comparisons and for identification of misconceptions about particular topics. Confidence as studied in our work to date has been c) the best predictor of achievement in both mathematics and English; d) is related to both cognitive and self-belief measures; and e) it captures much of the predictive variance of other self-beliefs that are, in turn, among the best known predictors of achievement. (Contains 5 figures and 6 tables.)