A child has not reached maturity and yet some of you want to impose this on him/her? How many of you wanted to be a pilot, the president, a princess or a king? Now how many of you have not gone down that route? Imagine what impact that would have on a child.
And anyways, if a parent helps a year 9 choose their GCSE options then they will probably choose entirely for the child. What if the child doesn't want to do that subject because it has nothing to do with what he/she wants to do when they're older?
As well as this, not being able to choose your subjects at a young age gives the child a base to build up on. Some general knowledge that might tie in with the subjects that he/she wants to do.
The idea of letting students choose classes is what I believe something that all teens should be able to do. Although general knowledge in all subjects is neccessary to succeed in this world, centering mainly on one topic will help you achieve more. Of course schools main purpose is to educate you and help you through your career. By the time people get to high school, teens should have a good idea of what they want to be when they grow up. The students should than take classes that will help them with the job. For example, if you want to become a politician, it is best to take classes such as gov. instead of english or math. If students could not choose their subjects, most would probably wouldn't learn gov.