Jeanie, did you know you can listen for 30 days? Archives, I mean. So - let's say you and your student fly near an airport with a CTAF (or tower) that is only busy on Saturdays around breakfast or lunch time due to a restaurant on field. Your student can go to the archives and listen to Saturday mornings. Otherwise, it is a "crap shoot" and you hear silence most nights if you listen to "live". Also, for example in my area, places aren't always clear, and they have a guide which has a map and shows you your area and what's transmitting, including frequency codes so you know you have the right one. Have fun.