I am training to be an English Teacher in High School.
As a learning strategy, Is it recomended to speak to students only in English once i begin my lesson or should i use examples and explanations in their native tongue?
Firstly, it depends on the policy of the school- some restrict any use of L1. If it's not restricted, there's a time and place for it I think, but it should be used as a tool and not overused.
I think it's not necessary. I always kept a rule in my classes that the kids can't speak their native tongue unless they raise their hand and ask. When I taught adults I was a bit more relaxed about that.