One year when I was a teacher, I had my students draw pictures showing some of the things we had learned during that school year. They drew the pictures on white paper, then held them over a window and retraced the design on the back with fabric crayons. Then I took the pictures and ironed them onto white fabric, stitched them together in a 4 patch and put them together with sashing. That little quilt brought in over $250 in a school auction, and that was 17 years ago!! I would suggest you decide on the size you want your blocks, draw a square that size leaving a frame for the seam allowances, and have the students draw the pictures on the paper first. You can erase on paper, if a mistake is made(spelling or just a miscue), a new piece of paper is much easier to work with than trying to fix it on fabric. Then, after the teacher has OK'd the student's drawing, have them trace over the design on the back with fabric crayons. They are doing most of the work for you & then you just have to find a pleasing arrangement and stitch it together. Also, if you have access to "room moms", I'd enlist their help.
I found that it helped my third graders to see me demo what worked best as far as a design--not a lot of details, more focused & clear. Also, we brainstormed a list first of what we had studied so far, students chose what topic they wanted to illustrate, and the drawing had to be approved by me first so I could check for accurace, clarity and spelling. It was a beautiful quilt!