Just to clear up some confusion, you are likely referring to MDM software like MobileIron, Intune, or AirWatch. MDM software CANNOT see personal messages, photos, or access your own personal apps. Schools (and companies) use MDM software to inventory devices, push profiles to simplify things like VPN access, SSO, and email configuration. It is also used to to push school related applications to the device and sometimes for remote diagnostics and support. IT departments and school districts are as uninterested in your personal information as you are in them having it. No need to worry.