Is the Respondus LockDown Browser required?

No. Installation and use of the LockDown Browser is not required for digital AP testing.  

The LockDown Browser can be used for the administration of practice assessments assigned within AP Classroom. There are AP Classroom–specific (and device-specific) versions of the LockDown Browser that teachers should be using if they want to administer secure practice assessments in AP Classroom. Sign in to AP Classroom and select the Guide for Teachers in the Help (“?”) menu to find instructions about the LockDown Browser.