Whilst the role of disciplinary literacy in science, technology, engineering, and mathematics (STEM) education is becoming more prominent, there appears to be little adaptation or allowance made for English as a foreign or second language (EFL/ESL) students learning science in English, as well as no clear understanding of what comprises disciplinary literacy in science. In this article, we define the construct of disciplinary literacy in science education and justify the use of the "Structure of the Observed Learning Outcome" (SOLO) taxonomy (Biggs and Collis, "Teaching for quality learning at university" 1982) as a tool for measuring EFL students' disciplinary literacy development. This SOLO taxonomy was trialled in a STEM integrated astronomy course enhanced with a digital storytelling approach. Data were collected from adolescent EFL students' written responses in their pre- and post-Astronomy Diagnostic Test. The results show a positive change in participants' science disciplinary literacy development and contribute to the understanding of the EFL/ESL students' science disciplinary literacy development and assessment.