Students with disabilities (SWD) have consistently been excluded in science in science classrooms. As inquiry-based instruction is the preferred method of science instruction, finding the best ways to teach using inquiry as an inclusive methodology is essential. The Science Writing Heuristic (SWH) is an argument-based inquiry approach that has shown to be successful for SWD. The current study examines the efficacy of the SWH in inclusive elementary classrooms for SWD, specifically focusing on engagement. We introduce a theoretical framework for engagement for SWD across instructional needs. Additionally, the study analyzes behavioral observation data on engagement to evaluate the efficacy of the SWH for SWD. Randomly selected classrooms in treatment and control conditions across four rural midwestern schools participated in the current study. Teachers in the treatment group were trained in using the SWH approach for science instruction and compared to teachers in a control group who taught science using the district-approved curriculum and methods. Mean scores were compared between SWD in SWH classrooms and their peers without disabilities and SWD in control classrooms. Multiple statistical and effect size analyses were conducted. Findings suggest that the SWH is an effective instructional approach that supports SWD in classroom engagement.