The Silence is Deafening

I have a total of 47 students this intersession. I have 10 Thao's, 4 Vang's, and 4 Yang's. That's right, 18 of my 47 students are Hmong. They are lovely students; very conscientious, studious, attentive, and hardworking, but they just won't enter into the class discussion. I've tried everything to get them to participate, but I just get averted eyes and no response. I understand it is a cultural thing, but I sure would like to hear what they have to say. I believe it would really enrich the conversation.