Well, as a basic web browsing machine, it's probably fine. The real question is whether or not it's in good shape. Never have I seen more abused laptops than those owned by schools.

So, if you can see the thing in person before buying, and ideally play around with it a little first, do so. I'd also insist on something like a 30 day DOA warranty. Basically, if it dies a horrible death within 30 days, the guy will either give you another one or refund your money.

Expect that the battery is completely shot at this point and will only offer a few minutes of power at most. If that factors into how you want to use the system, you can investigate third party batteries, but be sure to add that to the total price of the system when making a decision.

Basically, expect that the system has been treated very poorly over the course of its life, and some things may no longer work very well like the battery and optical drive. Used laptops are generally not worth the trouble unless you can see them in person before buying.