Grid it out so they don't have to wait for one kid to put the outline in -
let a group (small) work in each of the grids - make a decorative frame -
good for those who don't have quite the talent to shade and darken the
inside picture - put your darks in last - I have spritzed before to make
chalk not dusty but if it is for only one day you don't need to do that.
You will be amazed how much chalk it takes.