Is teaching interest based banking system in school allowed for a Muslim teacher?
Yes, if the teacher doesn't teach in a way which promotes haram banking system.
For example if the teacher just teaches how the banking system works in a way which doesn't promote the haram banking system then it's okay. And if the teacher says something like you should take interests Blah blah blah, then teaching that subject will be haram for him. And the teacher should teach his students about disadvantages of taking interest and how it makes the poor more poor then it will be definitely halal for him because he is telling his students to stay away from haram things.
Why not? Before judging if Haram or Halal one has to understand what is interest and how financial institutions use it. In my experience it is better to wait for students to be at least 15 years old.
Yes, the banking system is Haram. If you read history, you will understand that all market krach were caused by the actions of banks. In 2008 and 2009 the financial markets had a krach because the banks sold bad investments to investors telling them that these investments were good and safe. They lied, that is haram. They stole money from millions of innocent people when they cheated, that is also haram.
But the original question was not about banking or interest based banking system, the question was about teaching the banking system.
One cannot love without knowledge. Why is interest considered haram? If you love your children, teach them, show them why interest is Haram and why Allah tells us, with love, that we should not deal with people who use interest to profit by lying and changing the balance they use in the markets.
It is not appropriate to talk about these things when a child is too young. I did teach my children about interest and Haram but only when they were old enough to understand the reason behind. I showed them because I love them I did not want their faith in Allah to be blind. Now my children can accept and love the very words of wisdom that Allah gave us about interest.
As Salaamu 3laykum,
In my understanding it would not be alright to teach a subject that is impermissible. So let's say for example alcohol. You start teaching others how to make alcohol. One might say I am not creating the alcohol but you are passing on forbidden knowledge. The Quran and hadith are all about light and enlightening our lives and not to bring darkness , delusion , deception into our lives.
Inshaa ALLAH there must be something else you can teach that would be alright to do.
And ALLAH (Glory Be to HIM) knows best.