There are two reasonable answers to this question.
(1) Right now. School's composition changes every day. Each person who is hired or enrolls, each person who retires or graduates, each absence or "tardy"-- each person who isn't looking and bumps into you just when-- each of these changes in our networks of conversations has a ripple effect. Each of you has a very specific impact on the conversations you join. Your absence has an effect too. As we've talked about throughout the year, the members of a network change its purpose, its topic/s of conversation, its working process, and the outcomes it achieves.
(2) Never. It has been said that institutions don't change; people do. You have grown a great deal this year, and this place is better because you walked its halls. Keep doing what works. When you are confronted by elements of the institution you can't change, use what you've learned this year to find, analyze, evaluate, collaborate on, and apply the best information humanity has to offer. Education institutions should work for you; when they don't, hack them to create better learning experiences for you and your peers.
Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it's the only thing that ever has.