Varies. A lot of NSRA clubs won't bother on indoor ranges, possibly also on outdoor ranges. Depends on who is shooting. Clearly on a guest day for instance you're going to have a hi-viz'ed RCO and probably a couple of other helpers hanging around in addition to your 1-on-1 instructors. Likewise if you're running a competition or have visitors, then you will have an RO making sure that everyone is singing from the same hymn sheet and understands the local range rules.
Conversely, for two experienced shooters quietly coming down and buddy-buddy shooting on a Thursday morning, it would be tedious to alternate between one person supervising the other. You just manage together.
Shooting on a military range is obviously military rules, and local rules would be stricter on a larger fullbore range where there's potential (for example) of accidental incursion by members of the public and you need dedicated look-out.
"A fear of weapons is a sign of retarded sexual and emotional maturity." Sigmund Freud
Shooting is my meditation