The study focuses on the assessment of young refugee students, and the role of language and parents therein. Low achievement at tests can stem from lack of knowledge of the content being tested. However, it can also be due to low proficiency in the language of testing. Additionally, poor communication between refugee parents and schools caused by language or cultural differences may lead to underestimation of children's potential. We investigated, first, to what extent the language factor affects the performance of young Syrian refugee students in the Netherlands in mathematics and, second, the validity of parents' judgements of their children's mathematics ability. A linear mixed-effects model with random intercepts per participant was used to analyze the data. Results showed that the students performed significantly better in their mother tongue than in the school language. Additionally, parents' ratings of their children's mathematics ability correlated significantly with the mathematics scores on both versions of the tests. The study confirms the value of linguistically appropriate assessments and parental assessment when accommodating refugee students.