Lately, six schools in Berlin have decided to bring "German-only" language rule into effect. However, not everyone shares their opinion of doing so.
In the first place, those schools are attended by a lot of foreign pupils and now they will be forbidden to speak in their own language. No one should forbid the way of speaking until it is aggressive or rude. Only when someone is rude or vulgar, the consequences can be held.
What is more, foreign pupils may fell discriminated. I understand that during lessons schools' rights should be obliging. Nevertheless, everyone should be able to speak the way they like after lessons.
In the defence of schools with "German-only" language rule, we should understand that in German schools we can be asked to focus on learning German especially. Both other German students and teachers would not understand a word from what Turkish say, and because of that, Turkish would say everything and no one could pay attention to it.
In conclusion, I believe such rules should not be held in any school. If the rights of the national minorities are limited, it could follow some negative consequences and disagreements.