Brief thoughts on "full English immersion" lessons

Just finished my first set of classes teaching at a new company. They hired me as a native English teacher to work alongside a Japanese teacher, so I'm supposed to use only English in my lessons. This also means that if the students (currently only children under 12) say something in class in Japanese, I'm supposed to feign ignorance until they struggle out any sort of pigeon English that I can respond to. It was surprisingly difficult to pretend not to understand Japanese and basically ignore my students this week.

I am skeptical that this is a more effective way of teaching English than what I usually do. Usually, I don't respond to my students until they first 1) try to piece together the sentence/question in English, or 2) figure out how to say their sentence/question or English with my help. Before reminding my students to speak in "English, please!", however, I'll always acknowledge that I've received their intention to speak out during class. With all the Japanese students to whom I've taught English, I have found students who are willing to speak up much less common than those who aren't, so I value that over some "full English immersion" experience. I mean to say, I think I'm sacrificing students who are not willing to put in the extra effort on their own (the same students who tend to be in class because their parents are making them do so) for the sake of calling the "full English immersion" program. Shouldn't the lesson be adapted to optimize the number of learning experiences for the student rather than to attract the most parents?