Children should be equipped at an early age for political thinking. If politics was a compulsory area of study in school, much more people would emerge as politically-aware citizens who will vote in a much more informed manner. It should be our responsibility to ensure that children don't become ignorant to political issues and disenfranchised as a result.
The classroom is an environment for learning, so of course politics should be discussed. A teacher should not necessarily impose their views on students, but they should absolutely create an environment in which students can discuss politics and how it affects their daily lives. Schools are for learning so politics should be welcome in the classroom.
It would be a cool thing if politics would be a part of a normal school curriculum. Young children are full of ideas about how they want their world to be, and it would be so refreshing to allow them to discuss their own ideas. It would encourage them to develop their thoughts and learn how to express them in a way that is persuasive. Children are the future, why keep them out of "politics"? It is their future world that they would be discussing, let them invent it.
In High School there is no reason not to discuss politics. By teaching children how to properly react and respond to political discussions we are preparing people to interact with each other and their government. By making politics "off limits" we are teaching children that our opinions are best kept to ourselves and things will never change.
I do not think politics should be talked about in the class, unless its about current events or history. It is not the place for it. When strong opinions start to be voiced people begin to be offended and it could lead to something that is not needed or wanted inside of a classroom.