It seems that when group events are viewed using the Schoology app on iPad, the option to RSVP is not visible. Nearly all of my students use schoology on an iPad or iOS device. This lack of function is disappointing.
On the iPad you can opt to "View Web Version" via the three dots in upper right corner. Short of fixing this problem, development team should at least integrate a default notice into in event app view alerting user that "RSVP function not available on app, to RSVP select View web version by tapping three dots icon in upper right corner".