Edited to add: this also has nothing to do with some students being “brighter”. Different kids have different learning requirements, and not speaking the local language is an obvious one, though not at all correlated with intelligence.
The end result is actually pretty bad. The more advance kids are bored, the ones who need a bit more help are completely lost, and only those who happen to be exactly in the middle actually get something.
The original idea was to level social distinctions, but in practice it just broke the school system and in doing so increased inequality.
And I don't think money is an issue. The problem with lots of immigrant children is mostly one found in cities, where there is typically more than one "second grade" per school. So you could easily, with the exact same amount of teachers, give English lessons to classes 2a, 2b, 2c, 2d and German lessons to 2e and 2f.
Schools get a number of "teaching hours" allotted based on the number of children attending that school (some children might be classed as requiring more hours, i.e. those with certified special learning requirements). It is universally accepted (except by the politicians setting those hours) that these are insufficient to actually provide the supervision and support to have the learning outcomes that are desirable and demanded by government/parents. They also do not cover additional (but foreseeable) requirements due to illness, etc.
No school actually has all of these teaching hours covered because there are simply not enough teachers to go around. Even if, by some miracle, 100% of hours are covered at the beginning of the year, every teacher that leaves during the year due to illness, pregnancy, etc. is pushing down coverage.
Because of the lack of actual teachers, the hours are also increasingly covered by people transferring from other professions. These are counted as full teaching staff, but are obviously not as qualified as actual teachers. Teachers are also expected to do a lot of stuff that is not teaching, i.e. school administration, social work, counseling, etc.
My personal guess is that in most schools, you would actually need about 130% of the teaching hours currently allotted to provide a quality education for all pupils, while schools in special situations (i.e. large migrant populations) would need probably more like 150-200%. In reality, the typical school probably has only 80-90% of allotted hours available (some of which are covered by non-teachers) with schools in special situations often having even less, because they are typically situated in places with more budgetary constraints/not a desirable workplace.
This. Biggest issue in all variants of Germany’s education system. Schools should have their own budget which they can allocate as they wish and be allowed to freely raise additional budget from private of public sources for their projects. They should also have a say in the salary of the teachers they employ.
In Germany, historically, all teachers are civil servants that can’t be fired and, hence, aren’t really held responsible for the outcome of their teachings. Especially in troublesome areas schools are left with often incompetent and lazy personnel make the situation for children even worse.
Providing different classes at the same school would at least allow some contact of those different groups of children, and in a similar fashion, contacts between the adult population.