If I decide to be a teacher, what courses should I take?

I am in a really difficult position.I am 15 and I really don't know what I want to do when I'm older. I have to decide what coerces I want to take at college before christmas. I really don't know what to choose. My parents are suggesting being an engineer or electrician..that sort of thing. The only job that I have ever really thought about is being a teacher. I know this isn't very imaginative! but I can see myself as a secondary school teacher when I'm older. The thing is I'm really not sure if this is me or not? And I haven't really told anyone and I don't want to suddenly spring it on my parents. There is nothing else that I am really interested in. If I do decide to become a teacher what should I do in college? Would I have to take A-levels? I should have had a careers interview by now but they are useless at my school!