Since it sounds like you'll be making this a few times, I recommend going on aliexpress.com and searching for 'ws2812 60' and pick yourself up a roll of about 5 meters of 60 led per meter strip, without plastic cover - just the plain uncovered strip stuff. It's easy to cut in to individual lights with regular scissors and I've just tested it now and found it is also easy to sew through. They have little via holes on the solder pads of the flexible PCB material, and the flexible PCB is soft enough that the holes expand very easily with a small needleneedle. I think you wouldn't have trouble using them with conductive thread. Make sure you get some quick drying clear enamel (nail polish is good) to cover over the connections too so the thread isn't moving around lots and making the lights glitch out. Adafruit have some great tutorials on this stuff. Another neat thing about this stuff is the non-waterproof lights often have an adhesive back, so you can peel off the tape and stick them down to your fabric, then sew them in to place with the adhesive keeping everything lined up well. It is also easy to peel the adhesive off if you don't want it.
AliExpress vendors usually send their products via fedex or dhl, so you'll get it in just a few days instead of the two months or so that dealextreme usually takes. DealExtreme gets their products from the same factories who sell direct on aliexpress, and aliexpress has a much bigger range, but you usually have to order larger quantities. 5 meters of 60 led per meter gives you 300 lights, for about $50 in total. It works out being about 20ยข per light - so much better value than all those flora/lillypad lights on hard PCBs which tend to work out at closer to $2 each. If you like playing with light, I promise you will like having a roll of these lights on hand. I haven't done PWM on a microprocessor in a long time! It's great to have LEDs which don't need any resistors, and I was actually paying more for my RGB leds before. ws2812 are so much better!
Many adafruit products which aren't their own custom designed in house PCBs just come from alibaba/aliexpress anyway, and cutting out that reseller will save you a lot of money if you can meet the minimum quantities required by aliexpress. If you're teaching a large enough class you may even be able to order components from alibaba, where factories will be happy to make custom designs for you in many instances.
