Science content remains a commonly overlooked academic content area for students with severe disabilities, including ASD and ID, despite recent research. The purpose of this study was to evaluate the effects of systematic instruction, such as prompting and fading techniques, implemented during whole-group science instruction for students with both ASD and ID. Three elementary-aged students with both ASD and ID were taught science content using systematic instruction provided during group lessons; effects were measured using a multiple baseline design across behaviors (i.e., science units) with concurrent replication across participants. Science content was taught to all three participants in group lessons using systematic instruction utilizing errorless prompting methods (i.e., constant time delay) and activities that are related to the unit content. Probes were used to determine baseline and intervention effects. The results demonstrated a functional relation for one participant with increased performing demonstrated for the remaining two participants, indicating that use of systematic instruction embedded within a group instructional format may be effective when teaching science content.