This article draws on an action research process carried out by professional learning and development (PLD) facilitators supporting teachers in New Zealand secondary schools. Questions about students' developing knowledge of academic vocabulary, especially for English-language learners, were explored as part of responsive PLD inquiries within schools. This article reports on the quantitative data from vocabulary testing for 2,642 students in 35 schools which PLD facilitators collated and analysed to inform teachers' in-school inquiries. Emerging patterns of increased academic vocabulary scores in relation to ethnicities, kura kaupapa education, home languages, length of time in English-medium schooling, and class type were shared with teachers. In particular, the capacity of bilingual students and Pasifika students to develop academic vocabulary at speed is shown. This study reminds secondary teachers to address academic vocabulary learning and to have high expectations of all students within our increasingly diverse populations.