Recent educational policy initiatives in Ireland have focused on improving outcomes in reading and mathematics among students, particularly those experiencing educational disadvantage. However, science achievement in Irish primary schools has received much less research attention, especially in the context of educational disadvantage. This article examines science achievement and its relationship to school compositional effects in primary schools at the national level, including school-average indicators of the school context, as well as examining factors associated with science achievement in three distinct categories of schools (those with high, moderate, or minor levels of educational disadvantage). The data are drawn from the Fourth grade Trends in International Mathematics and Science Study (TIMSS) 2015 database for Ireland. Multilevel analyses were implemented in a stepwise manner. Findings suggest the relevance of school contexts with regard to science achievement. Before including school-level contextual variables, students from ‘minor disadvantaged’ schools achieved significantly higher science scores than students from schools with ‘moderate’ or ‘high’ levels of disadvantaged. However, this difference disappears after controlling for predictors at the school level. The findings highlight the importance of the home environment, including early numeracy activities and skills before children start school. Results are discussed with regard to educational policy and educational practice in Ireland.