I'll just throw this in here. Tell the girls that they are responsible for making their partner a better player that day. Of course they will act confused and ask how they are responsible for another player? Tell them by giving good side/front tosses, being right there with the next ball nd encouraging the partner on the tees, etc. We have them keep a diary and the last 5-10 min they summarize the practice, good or bad, who their partner was and how each got better/worse that day. It makes them actually think and stay on task and you get feedback on how good your practices are to the players.