I distribute colored pencils with a hand-held sharpener in a used candy tin for shavings for each table of two. Before class, I do a mass sharpening on my electric sharpener. Between every 10 pencils or so I sharpen a #2 pencil and this seems to keep the sharpener working with my mass of colored pencils. I learned this trick at a conference and it seems to work for me.
Also, try to avoid the cheapest of the cheap colored pencils. They never seem to sharpen right no matter what method you try and the colors are mucky. I am happy with Prang for the price and of course Prismacolor for their lush soft colors.