Students conceive of assessment in at least four major ways (i.e., assessment makes students accountable; assessment is irrelevant because it is bad or unfair; assessment improves the quality of learning; and assessment is enjoyable). A study in New Zealand of 3469 secondary school students' conceptions of assessment used a self-report inventory and scores from a standardised curriculum-based assessment of reading comprehension. Four inter-correlated conceptions based on 11 items were found with good psychometric properties. A path-model linking the four correlated conceptions with student achievement in reading, while taking into account student ethnicity, student sex, and student year, had good psychometric properties. The conception that assessment makes students accountable loaded positively on achievement while the three other conceptions (i.e., assessment makes schools accountable, assessment is enjoyable, and assessment is ignored) had negative loadings on achievement. These findings are consistent with self-regulation and formative assessment theories, such that students who conceive of assessment as a means of taking responsibility for their learning (i.e., assessment makes me accountable) will demonstrate increased educational outcomes.