I'm a long time Unix/Linux guru. Just what Naisho said, I recomend Ubuntu since it's a simple straight forward installation and it's good enough for what you need. As far as high school student, there are many open sources out in the world, like if you need word documents, you can get OpenOffice free, have lot of good stuff compare to Microsoft Office. OpenOffice usually built in Ubuntu. It has pretty much everything you need in it. There are time to time, depending on how old the machine that may require some tweeking like video display that turned out too big, running at 800x640 resolution and need to adust to get it to 1024x800 (most common for older machine that is max resolution).
Other than that, there are many applications are free. The most common problem is when your system crashed or locked up, they don't know what to do next or how to fix it. Just have to google it and manually fix it yourself with all the complex command strings. It's not any easier than MS repair tools.
Overall, it's pretty stable and great OS...Ubuntu
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