To a science 'outsider', science language often appears unnecessarily technical and dense. However, scientific language is typically used with the goal of being concise and precise, which allows those who regularly participate in scientific discourse communities to learn from each other and build upon existing scientific knowledge. One essential component of science language is the academic vocabulary that characterises it. This mixed-methods study investigates middle school students' (N = 59) growth in academic vocabulary as it relates to their teacher's instructional practices that supported academic language development. Students made significant gains in their production of general academic words, t(57) = 2.32, p = 0.024 and of discipline-specific science words, t(57) = 3.01, p = 0.004 in science writing. Results from the qualitative strand of this inquiry contextualised the students' learning of academic vocabulary as it relates to their teacher's instructional practices and intentions as well as the students' perceptions of their learning environment. These qualitative findings reveal that both the students and their teacher articulated that the teacher's intentional use of resources supported students' academic vocabulary growth. Implications for research and instruction with science language are shared.