Yes, you can. It’s legal if done in accordance with Cal-OSHA Title 8, section 3657. http://www.dir.ca.gov/Title8/3657.html Is it smart or safe? That’s another question altogether.
Let’s face it. Most school districts do not have the funds to comply with the above regulations and they typically have not complied with fall protection training nor have they purchased the appropriate equipment. Furthermore, most school districts have not trained employees in rescue techniques in the event that someone does slip, falls and dangles in their harness.
To ensure that you are managing risk and reducing adverse liability to the organization, prohibiting the practice is probably best.