Seeking to increase conceptual understanding by sustaining adolescents' engagement and interest in secondary science classrooms, an intervention, the Engagement Model of Academic Literacy for Learning (EngageALL), was designed to implement a disciplinary literacy approach and organize instruction according to characteristics of student interest development. A central feature of the intervention was the Generative Vocabulary Matrix. The purpose of this mixed-methods study was to determine the impact of the intervention on 222 ninth grade biology students' conceptual understanding of a one-week biology unit, quality of learning experience, student engagement, motivational changes, perceptions, and academic vocabulary/language use. Using the Experience Sampling Method, quantitative and qualitative analyses, and scenario-based writing to measure effects, findings revealed that students receiving the intervention performed at significantly higher levels of conceptual understanding of biology content, engagement, motivational factors, and academic language/vocabulary use compared to students receiving traditionally organized instruction. Students' daily self-reports illuminated positive motivational changes during EngageALL instruction. Qualitative data revealed themes reflecting students' perceptions of the benefits of the intervention. Student conceptual understanding was associated with motivational factors and academic language/vocabulary use. Implications for secondary disciplinary literacy instruction and recommendations for further research are offered.