Likewise, why should German tax payer dollars go to pay for the welfare of recent immigrants to Germany when their own children struggle to advance?
That is the wrong question, though. It's not about immigrants per se, nor about any other problems that we or our children may have.
There exists the saying "Do not bite the hand that feeds you", and the question one should ask is "Why still feed the one who is biting the hand feeding him?". This is the one thing I find upsetting. The ones who do bite the hand are still being fed (the others I don't care about, they're absolutely welcome).
The issue with children struggling is that most teachers have a very clear red taint, so class goes by the slowest learner. Which, in my case, back in the 70s, was a boy named Mohammed who hardly spoke a word of German (born here to parents who lived here for 10 years at that time) and only went to school because the police would show at home and get him (school is compulsatory, they aren't kidding about that here). His main interest was getting into a brawl during breaks, of course only with children who were smaller than himself. I didn't understand back then, and still do not understand why everybody else had to slow down (more or less stop learning) and why such people were/are tolerated at all. Look, it's OK to be a foreigner, but if you grow up in a place and simply refuse everything, you might just as well be kicked out.
We had two other foreign kids in class, and there was no problem with them. One of them was a bit slow, but he was trying (and not as slow as some others), and he was a nice guy, too. The other was actually one of the best performers.
That issue isn't limited to foreign kids anyway, there was the big "dyslexia temorary fashion" back then as well. Every child that was lazy or a bit stupid or otherwise not learning was explained with "dyslexia", so it wasn't the child being lazy but an illness. Maybe there were really some dyslectic children among them, who knows (years later at university and during work, I started to wonder if 1/3 of the population is indeed dyslexic -- not few are struggling with truly elementary things such as when to set a comma and when not to, or differentiating "das" from "daß", or when to capitalize a word).
Eventually they introduced dyslexia classes for these kids which they had to take in addition to normal classes. But at the beginning, it was just going by the "class goes by the slowest child" scheme, and instead of pushing the slow kids, it was said that it wasn't their fault. Again, though, there's that thing that in one case you have a choice, and in the other case you don't.
Then again, when I went to the USA on student exchange at the age of 16, I was stunned how much worse everything can be. Both in respect of failing to know or understand the most elementary things (Linear equations, huh? What? Oh, the war is over? We won of course, didn't we. You got electric light in Europe?), and in respect of violence as well. I can't tell which is the more telling experience, seeing two boys sticking a third boy's head into a toilet for no apparent reason, or the situation that arises when two young "rednecks" in the bus talk of what to do with "the niggas" when they're unaware of the 6 people behind them who take serious offense on that word and are willing to demonstrate that dissent physically. The two and their 30 friends probably put up a burning cross in someone's garden the next night in exchange (I wouldn't know, but it's probably a fair guess). Concerning some of these experiences, I ended up kind of relieved that I did not live in the "best country in the world".