In the research, it was aimed to determine the level of anxiety and metacognitive awareness of secondary school students about mathematics lesson, whether these levels change according to gender and class level and examine explaining status of these levels in mathematical achievements. The research, designed on the basis of the cross-sectional screening method, was carried with 1553 secondary school students. Two-step clustering analysis, independent t-test, one-way variance analysis and linear regression analysis were used to analyse the data. The participants were grouped into three according to their mathematics achievement and into two according to their metacognitive awareness and mathematics anxiety. The metacognitive awareness of the students with high achievement was found to be higher and the mathematics anxiety was lower than the students in moderate and low achievement group. It was found that the metacognitive awareness and mathematics anxiety scores explain the mathematics achievement significantly. It was also determined that as the metacognitive awareness scores increased, mathematics achievement increased significantly; on the other hand, as the mathematics anxiety scores increased, the mathematics achievement was meaningfully reduced. In addition, it was found that the metacognitive awareness had less effect on mathematics achievement compared with the mathematics anxiety.