Writing in mathematics class has achieved widespread approval, if not widespread use. The National Council of Teachers of Mathematics advocates the use of writing in mathematics, and several hundred journal articles, book chapters, books, theses, dissertations, and presentations have been written about writing in mathematics. Most of these materials, however, have been subjective—some theoretical, some anecdotal, and many providing general or specific ideas about how to integrate writing into the mathematics classroom. Within this broad area, the specific topic of interest in conducting this research was the effect of writing on the cognitive, metacognitive, and problem-solving skills of high school mathematics students. However, too little research has been done on this specific topic to allow such an exclusive focus. Thus, all quantitative research on writing in mathematics from the middle school through the college level that was subjected to tests of significance was considered. Fifty-five studies were found that satisfy this criteria