The current study investigated the effectiveness of an intensive writing intervention focusing on mathematical reasoning through written expression. A group pretest--intervention--posttest comparison experimental design was used to implement a 12-lesson intervention, delivered through a combination of Google Classroom and in-person classroom teacher support, to fifth-grade students with specific learning disabilities (n = 19). Although underpowered, our results indicated the intensive writing intervention led to all students in the intervention group (n = 11) significantly outperforming the students in the control group (n = 8) on subtraction and division word problems requiring an explanation of their solution in written form. Additionally, student treatment interviews revealed the strategy was both enjoyable and helpful in solving and explaining their word problem solutions and the teacher provided insight into potential additional scaffolds to support the most intensive students. Lessons learned and implications for research and practice are presented.