You may find this presentation helpful in setting up the classic experiment where potato wedges are used for observing the effects of osmosis. You can view the experimental setup in the text and a lab sheet in the pictures, but you will need to determine an appropriate size for the potato pieces prior to assigning this investigation. There is also an additional osmosis activity involving sodium polyacrylate crystals, meant to be done while potatoes soak. Although this is missing a few pieces, there is plenty of supporting material here to help you successfully teach an osmosis lab.