We did this to make a Valentine's card for the Bishop, but it could work anytime during the year.
(Sorry, no pictures! Put it together late last night)
Fold poster board in half. Cover says: Bishop: The primary gave you a heart attack!
Inside says: We sang with all of our hearts today!
I had a clear jar filled with cut out paper hearts. I told the kids that as I saw them trying their very best to sing/learn the song, I would ask them to write their name on a heart and put it on our card for the Bishop, because they were trying with all of their hearts to do their best. The kids did seem to try harder, but it was also hard for me to teach and try to call on kids to put their names on hearts at the same time. Next time, I would have a presidency member picking the kids, so I wouldn't have to worry about it.