Existing research shows that high scholastic boredom is correlated with a range of undesirable behaviors and personality traits and that the main antecedents of boredom are being over- or under-challenged. No study to date, though, seems to have systematically compared students who are highly bored and low-achieving (thus, likely over-challenged) with students who are highly bored and high-achieving (thus, likely under-challenged). Hence, merely knowing that students are highly bored might be insufficient for drawing conclusions about students’ behavior and personality, without taking their achievement level into account. We, therefore, investigated if low- versus high-achieving students who experience strong mathematics boredom show different behaviors and personality traits. The sample consisted of 1,404 German secondary school students (fifth to 10th grade, mean age 12.83 years, 52% female). We used self-report instruments to assess boredom in mathematics, behavior (social and emotional problems, positive/negative affect, emotion regulation), and personality traits (neuroticism and conscientiousness). In comparing highly bored students (more than one SD above M, n = 258) who were low versus high achievers (as indicated by the math grade, n = 125 / n = 119), results showed that there were no mean level differences across those groups for the behavior and personality trait constructs, with only three exceptions: conduct problems and expressive suppression (higher for low achievers) and positive affect (higher for high achievers). In conclusion, our results suggest that high boredom can occur in both low and high achieving students and that bored low- and high-achievers show largely similar behaviors and personality profiles.