We created a new role that archetypes the student role. Users with this role appear to be showing up in the Attendance block as well. Looking in the Site Admin and permissions I don't see any advanced settings to decide which roles appear in the block. So checking to see if somewhere in the code the block picks users with a certain designation of "student" which may also be passed along to new roles archetyped off of the default student role. Working in 2.4 now soon to be 2.5.
Happy 
oodling!