How come I get a headache from the computer screens at school and not the ones at home?

It's based on refresh rates (example: 80 Hz), CRT monitors have a lower refresh rate than the newer monitors, so in some it can cause faintness, headaches, and even nausea.

Because the monitors at your school are likely of lower quality than that of your home computer, it is most likely an issue with the refresh rate. However, an additional factor to consider is the lighting source. Your school most likely uses harshly colored halogen bulbs which will produce a great deal of glare on the computer's screen, and by themselves cause headache and eyestrain. That coupled with a poor refresh rate, or a low quality computer screen will exacerbate your headaches.

It could be one of several different things, but you probably should be able to figure out the reason just by thinking about it. Is the text blurry? Is it small? Does it wave or move around? Are you sitting much closer to the screen?

If the text obviously doesn't look right (blurry, for example) the problem may be as simple as the refresh rate being too high or too low.

I have that problem, when i feel like i am going to lose concentration, i switch subjects. And start to write down little notes as a study. If it is that important why did you wait for the day before? That is adding a lot.of stress on yourself! Plus MAKE SURE YOU SLEEP! Your brain needs sleep to function 100%. Also relax while taking the exam, whatever you don't spend time stdying for READ! You will still remember a lot of it. Read it like a story. Good luck!!!

Yep, eye strain on the ol' CRT. If you wear glasses, you can get a coating that will help it somewhat. Otherwise, ask them to change the resolution or refresh on the monitors that bother you