Several questions: * are you using the Pulse Secure "Universal App" for Windows 10, which is downloadable from the Microsoft app store, or, are you using the traditional Pulse Secure desktop client, which is downloaded from the Pulse Secure gateway to which you are connecting? * Are you trying to prevent the Pulse Secure UI from starting, or, are you trying to prevent Pulse from creating a VPN connection?
Generally, there is no way to prevent the Pulse UI executable from starting when you log in. Your system administrator can click a checkbox to prevent the Pulse splash screen from displaying, but you can't tell the Pulse UI process not to be resident in the background.
Now, if Pulse is automatically trying to create a connection when you log in, then this could be fixed by asking your system administrator at your school to change the default policies.
Assuming that you don't know your sys admin or that the policies can't be changed, if you are using the traditional Pulse desktop application, you might be able to switch to the Universal App (go to the Microsoft store and search for VPN - you should see it). The Universal App is a bit more lightweight and might be more to your liking. Please note that the Universal App only works with certain Pulse Secure gateways and configurations, so it may not work in your school's environment - you'd have to try it.