This article reports on the effectiveness of an intervention using conceptual change approaches within challenging tasks, on the mathematics gains for low-performing year 3-6 students in in six primary schools. Quantitative data from PAT-Maths testing for each year showed a consistently large effect size of 0.7 compared to expected gain data from DECD [South Australia's Department for Education and Child Development]. All six experimental groups caught up with DECD expectations within one year. Over the two years, students from years 3-5 gained an additional 27 months of mathematics learning over the expectations and students from years 4-6 gained 29 months, indicating the potential of the approach for closing educational gaps for low-performing students.