Yes Kevin, speaking from experience, I agree with your mother. I made a huge mistake in my life as a teenager when I decided not to go to sixth form. Now I'm stuck here slaving away at a 9 to 5 job earning mediocre wages.
Mum, Dad, I'm not sure whether I should go sixth form. My classmates are going to a different college and I would rather just do that. Or maybe find a job.
I think you should, Joining sixth form will help you a lot once it comes to applying to universities as they will usually look for whether a student attended sixth form. It also opens up so many options for you later in life.