The purpose of this project was to examine the levels of achievement and metacognition in expressing mathematics understanding and problem solving processes by students in a second grade classroom when the students used writing in daily mathematics learning according to their scores on a mathematical problem solving assessment and individual interviews. This paper concludes that through daily writing activities that involve expressing mathematics thinking, problem solving, and the creation of word problems, students' mathematics achievement and metacognition increased. (Contains 31 references.) (ASK)