The flipped classroom (FC) is becoming an increasingly popular teaching method in mathematics education. However, few studies have rigorously evaluated its effectiveness, and less so in countries where students' level of mathematics achievement is low. In this study, we evaluated the impact of an FC intervention in Saudi Arabia, the country with the lowest level of maths achievement in the last iteration of the Trends International Mathematics and Science Study TIMSS . A total of 281 secondary school students received eight weeks of algebra training using either FC or traditional instruction, and were tested on algebra problems taken from past national standardised tests, as well as on a measure of self-efficacy. Students who received the intervention showed higher self-efficacy but no significant difference in maths achievement was observed. Students' and teachers' perceptions of the intervention were positive.