Had an interesting session where a student was painting with water. Innocent was engaged and painting, and then took it upon himself to crumple up the paper. Was this a time to correct him? We were somewhat conflicted, but given that he was engaged for most of the activity (and engagement is a challenge for Innocent), we measured it as successful.
Some of my students were rubbing paint brush too much on paper. This caused the paper to tear. I gave him another sheet to add on top of his and it was interesting to see the colors bleed together.
My highly sensory student started out painting on paper, but discovered it was more fun to paint herself! On a warm day, I just let her do it and changed her wet clothes afterwards.