Are high school students accurate in predicting test performance? If so, do their predictions explain variation in performance, even after accounting for other factors? We examined these questions in two testing contexts (low-stakes and high-stakes) among students enrolled in a high school advanced placement (AP) statistics class. We found that even two months before taking the exam, students were moderately accurate in predicting their scores on the actual AP exam (κweighted = .62). When the same variables were entered into models predicting inaccuracy and overconfidence bias, results did not provide evidence that age, gender, parental education, number of math classes previously taken, or course engagement accounted for variation in accuracy. Overconfidence bias was associated with the students’ school. Results indicated that students’ predictions of performance were positively associated with performance in both low- and high-stakes testing contexts. The findings shed light on ways to leverage students’ self-assessment for learning.