Hi, As it turns out I have spent some time in a glass shop. My advice would be to avoid Plastic unless you are very budget bound, as it is the cheap choice. Plastic is soft and would scratch and or cloud quite easy from cleaning. However you can cut it with a table saw so it is easy to size. If you go with Glass which is what I would do I would think about your options. I would think 3/16 or 1/4 plate glass would work and be cost effective. However if you think there would be a chance for the "Kids" to wack it with a hammer or something, then you would want to go with a safety glass type solution. Safety glass is required in cars and at stores in the doors you push open to gain entrance. the 2 choices would be Laminated or Tempered. Laminated could be cut and scraps could work for your project quite nicely. used for tractor window replacements, cut to size, from standard sizes. Laminated works like your windshield 2 layers of glass with a layer of plastic in between. it would be breakable but would stay together and not cut the kids who broke it. Tempered glass you could hit with a hammer and it would likely not break until hit Very very hard. However it has the unique feature where you need to cut it then temper it, I.E special order. A solution for tempered glass that may work would be replacement panes for a fire place front. they are like 4 to 5 inches by 14-18 inch. you would optimally procure the glass first then make the "window" from the size you have, as it cannot be cut. For a school you could ask the glass shops in your area if they have any "samples" of tempered glass, some do and that could be a cheap way out as well. If you can keep a good watch over the glass,, regular 1/4 plate would be cheap, cuttable, and scratch resistant. I would use a clear silicone to install it, so it has cushioned, sealed, seating in the hive, 2 wood 1/2x1/2 inch stops. allow 48 hours for curing, trim with a razor blade what oozes out. before installing bees into the hive. If weather is warm there you could just use window screen, the metal kind. then you have the smell and sound to add to the experience. the window then would need a door or shutter to close up that much air flow. over time the bees would likely propolize it as well so a seasonal swap may be needed.
Gray Goose