Educational inequality and mathematics achievement have been long-term concerns in England. However, most studies of inequalities focus on achievement across multiple-subjects, and studies of mathematics achievement gaps tend to look at a single test in a single year. This study provides an overview of mathematics achievement gaps in the last 13 years. Aggregate data for nearly 13 million pupils for Key Stages 1, 2, 4 and 5 are used to explore the achievement gaps by gender, Free School Meal (FSM) eligibility and ethnicity. The Common Language Effect Size is used as a measure of relative achievement for the different groups. The findings show virtually equal overall achievement in mathematics between boys and girls, but boys achieve more highest and lowest grades. In contrast, the gap for FSM eligible pupils is immense: at KS4 the average FSM pupil achieves lower grades than 66% of other pupils. Ethnicity achievement gaps show a generally consistent order, with Chinese achieving the highest average grades and Gypsy/Roma achieving the lowest. The gaps for ethnicity expand as pupils progress through their schooling. All achievement gaps have fundamentally remained constant over time, with the exception of a few ethnic groups whose relative achievement has increased. Overall, this study hopefully provides a reference point for future research that explores causes and ways to reduce the identified achievement inequalities.