I liked the idea. Having a little book that Justin, when he is old enough, can write in different math terms that he learns.
Let your child/student make their own math dictionary! Just make a new page in it every time there is a new concept or term to study. The student can write the term, write an explanation, an example calculation, or draw a picture of it − or all of those.Anyways, go there to read the rest of the post. Thought it interesting, and worth remembering. :)
Making such a math vocabulary book shouldn't take lots of time, because you don't usually encounter new words every single lesson in a typical math curriculum. The rest of the time the book can act as a reference or as a review medium.
There is one exception though, and that is GEOMETRY. In geometry, just about all the time you have new terms to learn. In fact, a big part of the geometry in elementary grades is simply learning the meaning of words such as parallel, perpendicular, trapezoid, vertical angles, symmetry, diameter, radius, circumference, and so on.