Background: Evaluations of effectiveness of educational reforms are often based on the level of improvement in student performance from one cycle of a particular assessment to the next. However, improvements in overall performance do not necessarily translate to improved equality. Indeed, improvements that favour certain subgroups of students can exacerbate educational performance gaps and thus, inequality. This research examines changes in equality of mathematics achievement and subgroup performance differences in Irish primary school students over time. Ireland constitutes an interesting case study due to the introduction of a new National Literacy and Numeracy Strategy in 2011, the initial implementation of which has been linked to significant improvements in student mathematics performance. This paper aims to investigate whether these improvements have been accompanied by improvements in equality. Methods: Using data from the Irish National Assessments of Mathematics and English Reading (NAMER) and the Trends in International Mathematics and Science Study (TIMSS) from the period before and after the introduction of the Strategy, the study examines (i) deviations in student scores, (ii) variability in achievement at student and school levels and (iii) performance gaps based on demographic and socioeconomic factors over time. Bivariate analyses and multilevel regression models were used to identify student- and school-level variables related to mathematics performance. Results: The results showed a decrease in variability in students' mathematics performance after the introduction of the Strategy; this decrease was statistically significant only for TIMSS. Additionally, there was a considerable decrease in variance in mathematics performance attributed to between-school differences over time. These findings constitute evidence of increased equality as performance differences between students and schools tended to shrink. Regarding performance gaps and variance in mathematics performance explained by background characteristics, this study provided mixed results. In NAMER, subsequent to the introduction of the Strategy, the performance gaps and variance in mathematics achievement explained by selected demographic and socioeconomic characteristics decreased considerably. However, this was not the case for TIMSS. Conclusions: The evidence provided by this study suggests that Ireland has made reasonable progress in addressing inequality. However, there is room for improvement, as a significant proportion of the variance in student mathematics performance is still explained by demographic and socioeconomic characteristics.