Well yes if they don't have the prerequisites then they can't progress. But there's no reason you have to have that exact set of lessons to learn algebra. There

Well yes if they don't have the prerequisites then they can't progress. But there's no reason you have to have that exact set of lessons to learn algebra. There's the books that you're given, you can read them yourself, there's other books by other people, there's videos, there's catch-up classes, there's tutors you can hire.