We're going to try a weekly checklist method this fall. I'm not sure how it'll work out, but I figure we can always change it if it's not a success.
I've prepared a checklist of all the things we should aim to get done in a week in order to accomplish our goals for the year -- so many math lessons, so many reading sessions, so many science activities, etc.
Then my daughter is going to decide what she wants to do at any given time, and we'll check things off as we go along, remaining conscious of what still needs to get done for the week.
My motivation for devising this method was to give her the flexibility to choose what she wants to do when, but still have us both be accountable for getting everything done each week.