I have done this drill before as an adult student in a clinic. Its purpose is similar to 7/11 in that we want to work on serve and return of serve simultaneously. But this game builds more of a sense of camaraderie between the two players because they are working together to earn points.
One player is serving with second serves; the other is returning cross court. As a team they are trying to see how many two shot combos they can complete with a total of ten chances. Team with best percentage wins.
Returner hits down the line
Server uses first serve
Adapted from TeachPE.com