I picked DCX at random from a huge number of surf schools and was hugely impressed. Erik Lillmars (plus dog) is a patient, thorough teacher, a grizzled surfing (and music industry) veteran who spends a lot of time ashore before taking you out. I was standing up within an hour though, and had a blast. If you're not a confident swimmer that's fine, just let him know. I can't recommend Erik highly enough.
2450 Koa Avenue (parallel to Waikiki beach, behind the faceless hotels)
+1 808 589 7560.
surfingoahu.com/
Google map: tinyurl.com/32kh9mf