Conscientiousness is often found to predict academic outcomes, but is defined differently by different models of personality. High school students (N = 291) completed a large number of Conscientiousness items from different models and the Big Five Inventory (BFI). Exploratory and confirmatory factor analysis of the items uncovered eight facets: Industriousness, Perfectionism, Tidiness, Procrastination Refrainment, Control, Cautiousness, Task Planning, and Perseverance. Correlations between these facets and the BFI revealed that all facets related strongly to Conscientiousness. Criterion-related validity was demonstrated by relationships between facets and academic outcomes such as grade-point-average, disciplinary infractions, and attainment of academic honors. Compared to BFI Conscientiousness, Industriousness and Perfectionism showed significantly stronger prediction of absenteeism and cognitive test scores, respectively. Results are discussed in terms of the usefulness of facet scores, the interpretation of personality scores for selection, and the development of intervention programs. (Contains 4 tables.)