Dumbledore I have found a kindred spirit at least 
OP's post illustrates how poisonous and mindset creating setting can be.
My DS's school set them the minute they entered the school in such an inflexible way that they ended up in the same set for everything (except maths who got their own sets...) so , although he was a talented linguist he was in set 2 to match his English abilty. Bizarrely, this also dictated his IT ste. he can barely switch a computer on...
At the end of a year in his set 2, the French department predicted hima GCSE grade D. Two years later he has an A and an A* in Spanish! So, it's just as well we paid that no heed .
Conversely, the rot set in in that year in Geography, which he had previously loved. he went backwards . the class had 32 students, over 20 of whom were boys. There was little aspiration and behaviour management was challenging for the teachers. he went form being well behaved and settled to unhappy and then to quite naughty.
He has just got a D in GCSE Geography . Hmmm...
Some schools will do a better job of setting than others, that said. But I still hate it.
As for your DS , keep an eye on things,especially a slide in motivation or attitude. We let it slide too much in hindsight. DS2 is going to the same school soon and we will be watching like hawks!