Three months ago at a family meeting we came up with a 'rule' for practising that actually worked, and that everyone was happy with. If you miss your practising, you don't play on the computer the next day. It was Noah's idea. We discussed this as a question of balance. If one day is balanced in favour of unstructured play and computer time, it makes sense to right the balance the next day and stay off the computer. During the first couple of weeks there were occasional missed practisings (sometimes Erin or Noah would only manage one practising on a particular day) but after that the practising was quite consistent.
But then the computer was out of commission for 3 weeks; the kids hardly missed it at all.... and interestingly they were just as good about doing their practising, even without the computer contingency. But then the computer got fixed a couple of weeks ago and we experienced a bit of a novelty effect. And this week at our meeting they asked for a change to the practising and computer rule. This week they want a maximum of an hour at a time on the computer (then they must take a break and let others take a turn if they wish). And they want to do their practising without reminders, pressure or coercion. And, of course, if this doesn't work, we deal with it at our next meeting and change the rules.
So far Erin has mostly practiced just fine. Noah has practiced about half the time, and Sophie has missed three or four days in a row. I have managed to stay pretty low-key and am determined to wait out the week, no matter how abysmal, and see what the kids decide at next meeting. I know it'll be clear to the younger two that this is not working. An imposed solution will not be as effective as something they participate in coming up with.