The present two-wave longitudinal study investigated the accuracy or bias in students' math self-concept of ability during the transition to high school from the last year of secondary compulsory education (10th grade). The role of students' gender and parents' educational level in predicting the accuracy or bias in math ability self-concepts was also investigated. 424 Spanish students participated. The results analyzed with the person-oriented I-States as Objects Analysis (ISOA) showed four groups of students: high-accurate, low-accurate, optimistic, and pessimistic. Males more likely belonged to the high-accurate or optimistic self-concept math ability group. In addition, students whose parents had a high level of education more likely belonged to the low-accurate or pessimistic self-concept of math ability group.