Medical research is held as a field for education to emulate. Education researchers have been urged to adopt randomized controlled trials, a more "scientific" research method believed to have resulted in the advances in medicine. But a much more important lesson education needs to borrow from medicine has been ignored. That is the study of side effects. Medical research is required to investigate both the intended effects of any medical interventions and their unintended adverse effects, or side effects. In contrast, educational research tends to focus only on proving the effectiveness of practices and policies in pursuit of "what works." It has generally ignored the potential harms that can result from what works. This article presents evidence that shows side effects are inseparable from effects. Both are the outcomes of the same intervention. This article further argues that studying and reporting side effects as part of studying effects will help advance education by settling long fought battles over practices and policies and move beyond the vicious cycle of pendulum swings in education.