well I disagree with Pete on this.
Lets say I have Pete's list of the most important things to practice, you formulate a program to work on this at the weekend. You turn up, no-one else is there. You're just standing there with your clipboard looking all bemused........you go home.
My point is, that even if they had in fact been called, and were there, if you can't communicate, how are you going to be able to tell them what to practice? I suppose you could just show them the list, but that in itself is a form of communication, as is body language - so pointing and so on would also be out.
No, communication is definitely the top thing in my book.