I store my paint filled egg carton sections in a shallow tub with a lid until the section uses the paint. The egg cartons get a little soggy after a while, but works great for about a week period of time. Saves on paint waste!
31 Genius Hacks For Your Elementary School Art Class
MANAGING THE ART CLASSROOM: PAINTING ORGANIZATION & CLEAN-UP. These tips are great if you teach in students with special learning needs or fine motor challenges. Read more at: http://artteachershelpal.blogspot.com/p/painting.html
Two For Blue- "Experimenting with color: This tray started out as two pools of yellow and two pools of blue. The rest were just water. The artist learned to use a dropper and saw how many colors of green they could make