The most effective conditional clincher for Chelsea's essay is:
If teachers don't learn that homework has little benefit, students will continue to be stressed out and sleepless, which will not allow students to take the time they need for themselves.
This statement effectively ties together the argument that homework is harmful to students with a prediction about the future consequences of not changing the current system. It implies a call to action for teachers and highlights the ongoing impact that the current state of homework has on students' well-being.