Can you assign specific sections for students to complete or must they work in the order given?
Right now, the tree must be done in order. We realize this is a feature teachers would love to have, and it is on our list of features to investigate.
The bright side is that the order of Duolingo's trees are scientifically tested and known to work well. We are constantly running tests to find improvements and update the trees accordingly as soon as we make new discoveries. We also adapt to each student's needs—every student takes a placement test and moves forward at their own pace, with us presenting them with the right challenge level to help them learn without getting bored or discouraging them by making it too difficult.
Duolingo for Schools gets updated often and has changed a lot over the past few months... this is going to keep happening so I recommend checking it out often and keeping an eye in these forums, which is where we will announce new, shiny highlights. =]