But that makes no sense - believing you can solve an equation doesn't help. You have to be able to do it. If you can't, they pushing you on to harder and harder equations is pointless. The teachers will be doing their utmost to make sure the child CAN solve the basic equations, and once they can demonstrate that, they'll be taught how to do harder ones. They need to have enough time to learn that before the exam, though. They will start the basics of the curriculum early, and when they are able to do those topics well, the teachers will build on them. It's in all their interests to get children as far as possible, but pointless to force them to sit through topics that are beyond them at that stage. It's not saying that they're beyond them forever - as soon as they can and do demonstrate mastery of the basics, they will be taught harder stuff. You're not holding them back from higher level topics that they might magically be able to do if they just believed in themselves - if they can't do the basic steps, you need to teach them that, and teach it well. And yes, encourage them to believe that they can do more.
Obviously some of it depends on how the timetable and sets work at a given school; you can't be forever moving people at a completely individualised pace for every topic, and there does come a point where decisions have to be made overall about which is the best paper.
but unlike some subjects where confidence and belief mean that you could suddenly tackle harder topics whether or not you've done well in lower years, maths means you do still have to learn the lower stuff and show you can do well in it. Once a student can do that, then they should be moved up and given the chance for harder work.
I do have a pupil I tutor doing foundation maths who i think would be capable of higher, and who just doesn't show what he knows on exams. And has very slow processing speed, to boot. But that is a different issue. He does in fact understand the lower level stuff, and I think could be moved on, if there were an assessment that allowed him to show it. It is compounded by the fact that at his school, there is very little set-changing, and only once a year, so you do run into problems of running out of time to be taught the higher stuff, once you've demonstrated you can cope with the lower level material. And I do think that is wrong.
But that's different that just saying that all children should be taught the higher level stuff just in case they turn out to be really good at it - they need to demonstrate some understanding on the lower level stuff first, because it all builds on those skills.
I'm all for not limiting a child - encourage them to show what they can do, to do well in their current set, and to have the chance to move up to harder stuff - but it doesn't mean that higher sets are right for every child. If you spend too much time trying to learn harder stuff that you don't understand, then you are in danger of not having enough time to really solidify and practice the more basic skills - and then you can end up with nothing.