Strategies instruction has improved the writing of high school struggling writers in previous studies, including students with disabilities. This study examined the effectiveness of argumentative writing instruction for the ACT writing exam using the Self-Regulated Strategy Development (SRSD) model with high school students with disabilities or at-risk for writing difficulties. Using a multiple baseline across participants design, four 10th grade students (three males, one female) were taught to analyze ACT prompts, plan, and write an argumentative essay using the SRSD model. Following instruction, students increased quality of their plans, number of argumentative elements, overall ACT essay score, number of words, and number of transition words in their ACT essays. Students were positive about the strategy, learning process, and its effects.