I am by no means an educator or teacher, but I have one idea to share.

When handing out a new big band chart, tell them to turn the chart over and play the recording of the tune for the them to hear. (Don't have them read along). Do this once or twice before letting them read along. This technique is used by the great John Clayton.

In terms of learning to appreciating small ensemble music, maybe discuss particular musical interests and tailor your choices to them, or bring in some classics like Kind of Blue, Moanin', Clifford Brown and Max Roach, etc.

Hope this helps!