This article reports the findings of a study designed to examine the influence of multimodal writing on the communication of mathematical ideas. Elementary school students (ages 8-13) were required to write mathematics notes using two digital writing technologies, a personal digital notepad and a social mathematics blog, in the context of a formal intervention. Forty-two students participated, across three schools. The study showed that when students wrote notes that could be assessed for correctness, their answers were predominately right, indicating that mathematical sense-making was taking place. It also showed that the digital notepad and blog were used differently and that the type of technology influences the writing content. Moreover, students' mathematical writing were understandable by their peers and students collaboratively explored solutions. Younger students were more likely to draw pictures to represent their ideas than older students. These findings show that writing can help students acquire mathematical understanding, and suggest that multimodal writing may help them surmount difficulties often associated with learning math. Although this research demonstrated that writing can help teachers gain an awareness of their students' mathematical understanding, it also revealed that writing environments need to be monitored and students require close guidance to bring about systematic improvement.