Knowing the pupils’ metacognitive skills represents a challenging task for many compulsory education teachers in different school levels and various disciplines. The main purpose of our study was to investigate how math competences of elementary school subjects are related to their metacognitive monitoring accuracy. 112 second grade elementary pupils were examined with a math test and they also provided an estimation of their own result. The discrepancy between the estimated and the actual score offers a measure of their metacognitive monitoring accuracy. The results show that the lower the score, the optimistic the pupil’s estimate is. The best performing students show a good calibration. Some educational implications are discussed.