Federal legislation requires every student receive access to and make progress in the general curriculum. Teachers have reported difficulties in meeting this requirement for students with extensive support needs (ESN) who do not yet demonstrate foundational academic skills, such as in the areas of literacy and numeracy. Once students enter high school, the gap between the mathematics skills a student currently demonstrates and those required to engage in grade-level, standards-based mathematics, widens considerably. Researchers have evaluated different interventions to teach both foundational and grade-level skills to students with ESN in the area of mathematics. This study builds on that research by evaluating the effects of an intervention package comprising modified schema-based instruction (MSBI) and embedded simultaneous prompting (SP) to teach secondary students with ESN who do not demonstrate numeracy skills to solve simple linear equations (e.g., 3+x=9) and to identify numerals 1–9 concurrently. The experimental design was a single-case multiple probe across numeral sets replicated across participants. Two high school males with ESN participated, along with instructors, a paraeducator and a special education teacher who implemented the intervention. The intervention was not effective for teaching numeral identification or solving simple linear equations, nor did the students generalize numeral identification to real-world settings. However, the instructors did find the study procedures to be socially acceptable and hypothesized that the students would eventually reach mastery criterion, given additional time in the intervention. The findings from this study can be used to guide future research designed to support the needs of secondary students with ESN who do not yet demonstrate foundational numeracy skills.