The co-teacher has a very active role beginning in TK and Kindergarten which lessens somewhat each year as they progress in elementary. Each student is different, therefore the time and role of the co-teacher varies.
The co-teacher is a guide for dependent study. Middle school students want independence but should still be closely monitored by the co-teacher who provides extratutoring in weak areas and makes sure assignments are done correctly and are turned in on-time.
At the high school level, the co-teacher is a guide for independent learning. During the high school years there is less focus on teaching and more emphasis on supporting the student to be an independent learner.