I did a project like that a long time ago. My sister handled the logistics from Germany and I had her hand out pieces of paper cut to the correct dimension. Each kid drew on the paper the message they wanted to send the teacher. Some were more creative than others. My sister sent me the papers and I scanned them into the computer and printed them on fabric. I liked that better because it gave ME the control over ALL fabric-related processes.
Unfortunately my PC crashed and I lost the pictures but it turned out soooooooo darn cute. I used kid/teachery fabrics in the sashing.