The purpose of this research is to examine the comparability of mathematics and science scores for students from English language backgrounds (ELB) and non-English language backgrounds (NELB). We examine the relationship between English reading proficiency and performance on mathematics and science assessments in Australia, Canada, the United Kingdom, and the United States. The findings indicate a strong relationship with reading proficiency accounting for up to 43% of the variance in mathematics and up to 79% in science. In all comparisons, ELB students either outperformed NELB students or performed at the same level. However, when statistical adjustments were made for reading proficiency, in both mathematics and science, the score gap between the groups became statistically non-significant in three out of the four countries. These findings point to differences in score meaning in mathematics and science assessments and limitations in comparing performances of ELB and NELB.