A free ‘massive, open, online course’ (MOOC) designed to change students’ attitudes towards mathematics makes them more engaged in class—leading to significantly higher test scores. Published in open-access journal Frontiers in Education, these findings go against the discouraging results of previous studies. It is the first of its kind to show the impact of an online course in changing students’ mindsets and beliefs about mathematics and their achievement, with the potential for more widespread dissemination.