This is not a lesson plan but an interesting way to motivate students to speak French in immersion classes. Staple it to a large bulletin board.
Students start off with ten leaves which they staples to their branch.
If they speak French during the day they earn more leaves. If they speak English when it's not English period, a leaf falls from their branch. If it is Fall the tree can look quite colourful. The teacher can add a nest and birds to various branches as a sign of extra good work or effort. Of course, there are many variations to this idea.