This study aims to investigate the effect of the online flipped learning model (OFLM) when integrated into a mathematics course in an emergency remote teaching process on seventh grade students' academic achievement, their attitudes towards their mathematics course, and their cognitive load. The study was designed as a crossover experimental research model and conducted in two stages. In the first stage, 26 girls constituted the experimental group and 22 boys constituted the control group. In the second stage, the experimental and control groups were switched. In both stages, an academic achievement test was administered to the groups before and after implementation, an attitude test towards the mathematics course was applied to the experimental group before and after each stage, and a cognitive load test was administered to the groups after the live online classes each week. Also, the students' views about OFLM were obtained through qualitative methods. The findings indicate that there is a significant difference between the academic achievement of the experimental and control groups in favour of the experimental group in the first stage. However, in the second stage, no significant difference was found between the groups. Students had a more positive attitude towards the mathematics course when the flipped learning model was used. There was a significant difference in favour of the experimental groups in the cognitive load of the experimental and control groups in both stages except for the first week. This study provides evidence that OFLM contributed positively to the mathematics learning of secondary school students in distance education.