First off. Starting fluids like ether, WD-40, etc. are NOT for normal use. If you do use some DISCONNECT THE GLOW PLUGS FIRST! You don't want to blow up a precombustion chamber !

As for the starter. A weak starter may be enough power in warmer weather but in cold weather it might not have enough power to crank fast enough.

Don't forget, the glow plugs stay on 45 seconds AFTER he light goes out. Let them go for about 20-30 secomds before you start. If the school will let you go out to your car between classes or lunch, go start it and run at 800-900rpm for a few minutes. In an extreme times, get a remote starter. With this you can sart it from class or set it up to auto start every 4 hours. Most have a glowplug delay feature for diesels.

BTW, what city in OK do you live in?