Why Use Math Journals?
While students learn how to "do" math, they must also learn how to articulate what they are learning. It is important to provide many opportunities for students to organize and record their work without the structure of a worksheet. Math journals support students' learning because, in order to get their ideas on paper, children must organize, clarify, and reflect on their thinking. Initially many students will need support and encouragement in order to communicate their ideas and thinking clearly on paper but, as with any skill, the more they practice the easier it will become.

Journals also serve as invaluable assessment resources that can inform classroom instruction. Reviewing a student’s math journal provides a useful insight into what a child understands, how s/he approaches ideas and what misconceptions s/he has.

Resource:http://www.k-5mathteachingresources.com/math-journals.html