Content writing contributes to students' positive learning and outcomes. Mathematical-content writing has been shown to positively support students' mathematical reasoning, but it is challenging for many students with and without learning disabilities. This study explores proof-of-concept evaluation to extend self-regulated strategy development, an evidence-based practice in writing, to mathematical content-specific writing. Twenty-seven students participated in this pilot study, which included seven students with disabilities. The intervention consisted of six lessons that taught students a strategy to self-regulate written responses to open-response mathematics problems. Results indicate that mathematics fact fluency correlated with mathematical writing quality and demonstrated to be a potential predictor for mathematical writing performance. Mean scores indicated that students in the treatment group outperformed students in the control group, although the difference was not