When I glaze with my students (I currently only glaze with third grade and older) I have smaller containers of glaze all ready to go and set up on a counter in my room. Each container is labeled with the name of the glaze and a photograph of what the glaze looks like when fired. Students are to take a new brush every time they change to a new color. Dirty brushes are placed in water buckets at their work stations. Last year was the first year I used this system, but I did use it again this year with the pinch pot frog lesson we are currently working on. It really does make glazing so much more manageable for the class room setting and allows students to have more say in color selection for their projects.
I try to have three containers of the same color to help with the sharing process.