I thought about suggesting a tablet, but he is talking about doing a school exchange and then travelling. I don't think a tablet is a viable option for real school work at this time, unless you are talking about a Windows 8 one, with dockable keyboard, which certainly wouldn't be a cheap machine, imho.
My suggestion would be an entry level 14" ultra book, like the Vostro 2420 or 3360.
You can get a
2420 for $350 to $430 or a
3360 for $560.
The 2420 is more of a netbook type machine in that it is a little less powerful, which is reflected in that price point, but the 3360 has an i3 and 4GB ram, which makes it a fairly decent machine for the money. Both are very small and light, which for travel should be a primary concern.