Alright, here's what you're going to want to do. Follow these instructions carefully and you'll quit getting erections in class.
Step 1: Get a picture with the girl you're sitting next to, preferably straight on. This might be tricky, but do it so you don't look like a total creeper.
Step 2: Take the picture and get it developed. Ask the man/woman at the photo center to blow up the size of her face to life size.
Step 3: Attach the photo of her face to the end of a pillow, long ways. Then with a knife (make sure you have supervision) cut a nice slit in the other end of the pillow. Make it a snug fit.
Step 4: Insert your penis into the slit and thrust it till your fantasies are lived. Then, when you see her at school you won't get turned on by the bitch anymore.
Tips: You can add arms and legs to the pillow using tube socks filled with bags or crunched up newspaper. This will add to the reality of it!
Have fun, be safe, and most of all enjoy your home-made creeper sex toy.