Pallas, get a bag of shrimp at the store. Size doesn't matter, nor cooked v. raw condition. Throw one, or two if very small, into the tank. Make a nice shrimp cocktail for dinner with the remainder. That's all there is to it.
You might want to make sure the deceased is hidden behind a rock, wood or plant, either weighted down or otherwise kept where it won't drift around and become visible. The kids might get the wrong idea about things.
Re: purity of ammonia, don't worry about it if all you can find is a watered-down version. Just make sure it doesn't have detergents, surfactants or other cleaning chemicals added. You can usually find it in the cleaning-products aisle of a reasonably stocked supermarket, probably by the Clorox and 20-Mule Team Borax and other old-fashioned cleansing products.
No soap or detergents of any sort can ever be used in any tank, it is deadly to fish and other tank life. Oh, and don't use anything containing copper, either in medications or in solid form as in decorations--that is lethal to shrimp.
As to the blue gourami....ouch. A parental donation no less, she'll be expecting to see it. Either you or the teacher is going to have to thank the parent profusely and then gently but firmly decline the donation. Use any of the argumen...er, I mean knowlegeable discussion points found in this thread to explain why it is not suitable for a 10g tank of the sort you want in the classroom.
have fun with that.