One thing I have done for our musicians is applied this simple line...
"Practice" is at home. "Rehearsal" is the next time you see me...
Also at rehearsals we don't go over the songs, as in, "What are the chords for verse, chorus, bridge etc?" This is something I apply for rehearsals - no learning of music during rehearsals, period. They are given the music to take home to "practice".
When at rehearsal, they have the option to either play the song, sit there like a statue or if they feel the need - leave. I won't ask them to leave... its up to them.
This method may not be the best solution but it works.