Mathematicians at Work?!?

Yesterday I blogged about my writing bulletin board on which a monthly writing sample is displayed for each student.  It is actually like a portfolio, but on a bulletin board.  I would like to do the same thing for math.  Here is what I am thinking:  I could focus on problem solving.  Each month I would collect a sample from a student and display it on the board.  Last  year I started to work with my students on explaining their thinking during math talks.  Then we progressed to having them write their explanations down.  Hmmm .... I am thinking that this would make for a great way for my students to see their progress in problem solving.  Then at the end of the year, each child could put their samples together in a booklet and take it home as a math portfolio.  Hmmmm .... more thinking on this needs to be done!