A TOEIC Class

I am teaching a class for the preparation of the TOEIC test, which is an English test for business people in the world. In my class, I give an instruction in English because a TOEIC study is part of the bigger picture of English education.

This, however, may not be how my students think. They may not like an English only class if they do not understand the language well.

So, yesterday, I gave a TOEIC class in Japanese, the mother tongue of my students. The class atmosphere was much livelier than the usual. There was a new-born rapport between my students and I. They asked me questions. Even the most reticent one in the class asked me questions. 

Now that I know they are happier if they are allowed to speak Japanese. A question is if I should follow suit. My concern is that the quality of English education may suffer if the Japanese language is allowed.

An imaginary voice in my mind says, "Don’t worry about the quality of education. If your students are happy, let it be. Don't lose our job for your belief. Your life is more important." 

Is it true?