The Starting Gun vs Freedom of Choice
I think that the assumption of the question is overly deterministic. I am also pretty sure that I'm a living counter-example, though my case won't prove much. I was a terrible student into about 10th grade (say age 15), especially in math. My teachers once wanted to hold me back because I hadn't learned my multiplication tables. A plane-geometry class was my first positive educational experience of any kind. A bit later, a writing course appealed to me. Up until that time, I would rather have been anywhere but in school. 

I was also told once, in high school, that, based on a standardized test, I probably wouldn't be successful in College and so should set my sights lower. 

I later earned a PhD in Mathematics. 

But there were no jobs for mathematicians at that time so I taught myself programming, with plenty of halts and stumbles. Then some deeper Computer Science. Still later I was lucky to have been mentored by some of the CS superstars in education. 

But my early history would predict none of that, nor were my teachers particularly enlightened when I was young. 

I worry about the question from another standpoint also. I don't think many individual teachers have much power over the overall curriculum. Groups and associations can make a difference, however, but this site doesn't really help with that sort of question. 

However, if you are a teacher, you must not have a defeatist or deterministic attitude about your students: they can't learn so why bother. Every student in front of you, given some desire, can learn. You  have to be there to help them. You may even need to teach them how to learn in general, since their background may be like mine was. I eventually got desire, and the rest followed. Your job as a teacher is to educate them no matter what their background, be it advantaged or disadvantaged. The prime directive.