The Progressive Achievement Test of Mathematics (PAT: Mathematics) provides norm-referenced information about students’ level of achievement in the skills and understanding of mathematics. This knowledge guides teachers’ decisions about mathematics teaching programmes and aligns with the current evidence-based approach to teaching and learning. In practice, these assessment tools are also used to inform overall teacher judgements (OTJs) when reporting to parents and to the Ministry of Education against National Standards in numeracy. This article sets PAT: Mathematics within the context of literature on the assessment of English-language learners and reports on one teacher’s exploration of an English-language learner’s experience in sitting PAT: Mathematics. The findings indicate that teachers and schools should be cautious about interpreting results when English-language learners sit assessments developed for native English speakers.