We teachers of English or another language are making something grand, which is to set an instrument to communicate with other people.
Because of that, tentatively classes should be in English, so as to foster real communication.
In our today’s global world our students soon will have to communicate with people from other countries, not necessarily with English as the first language.
Thus English is a vehicle for that communication.
We can have our students think of all this, for them to realize that English is something useful. Conduct all the class in English. Even if you have to announce something, do it in that language. This is ok with levels of some advanced grade or fluent linguistic competence. / Photo from: www handstrack com