Spongelab is a awesome resource for science lessons, image, interactives, and lesson plans. Using Spongelab you can create a class that students can join by creating accounts (which can be done using their Google Apps accounts) and then entering in your class code. All of this is demoed in the tutorial above.
All in all, Spongelab is a great free, that's right, free website that can be a great supplement to your science curriculum.
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