I don't think there's anything wrong with making a website for your school. As you are not a "commercial programmer", your client is NOT a "commercial client", therefore you are (as per today) a hobby programmer and your client will like whatever you will make them (for free).
Don't get me wrong. I don't mean that in a nasty way. What I'm trying to explain is that there is a difference between being "technically" capable of something (building a website) and doing this as an assignment where someone pays you for it. This is known as "experience".
And yeah, sometimes clients are idiots..