He offered his school to help create the school website because it would be fun and good practice. However, it turned out that creating a website for someone else isn't just doing the fun bits you're interested in or tinkering with the tech you'd like to know more about. Suddenly there is a client and this client has requirements and expectations. If you not used to this you might be in for a surprise.
For all the 17 year old's reading this thread; There is a big difference between programming for yourself and programming for someone else.
I learnt this the hard way when I was 16! Clients can be plain idiotic sometimes!
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..
And just to mention: NEVER create a website for your school :D