I have several younger students that I use play therapy with at the end of the session. We do an activity and good speech sounds are required. If misarticulated, they are required to fix/repair errors. It is 100% application of skills they need to learn to use new sounds and apply while doing someting else. Older kids I do the same thing with motivating activities like say something conversationally with good speech and earn shots at basketball hoop, etc.