I would read through a few of the posts in the Belize forum on San Pedro. That forum may also get more responses on dive ops for kids/15 year olds. There are hotels that have associated Dive ops in San Pedro, Ramon's is one. But really San Pedro (From airport on south to small bridge on north) is really small and golf carts are the main transport. Google satellite view will give you a good feel. With a golf cart you should be in easy reach of several dive ops in downtown. So where you stay and where you dive do not have to be very linked. I saw you dive, so presumably you may be going to the dive op as well anyway. San Pedro is a nice laid back place. My only hesitation would be needing more shallow dives, but I'm sure they have many OW students as well, so it should be something they can handle.
There appeared to be several vacation resorts north of town, and one next to WhiteSands dive shop. All the shops advertise picking you up at your dock. So getting junior to the shop in the morning may be even simpler. Wave good by after early breakfast, come back by lunch is likely an option most places. (I have nothing to do with anyone in Belize, I just spend a nice week there and liked it.)
Edit: add the below.
White Sands chose to use Amigos del Mar (in down town) for their Atoll trips.
In prep for my trip I found the posts of peterbj7 most informative,
Ambergris Caye dive operators.
Below are some of my notes, listing dive ops I found. Note that one had a pool, could be very useful for private class.
“Most of the diving off Ambergris Caye takes place in the AOW region, between 60ft and 100ft.” - quote from some post, likely by peterbj7, which means at least the dive sites, it might not mean the dives.
Island Divers (San Pedro bit south of airport south end)
Rudy belizeislanddivers.com/ was IslandDiversBelize.com
by Grand Colony Island Villas 5012264800 south of airport
rudyislanddivers@gmail.com
Learn: OW 450, elearn 350, referral (2 days, 4 dives) 280
AOW (5 dives) 380
Ramons (San Pedro airport north end)
Scuba Diving info@ramons.com Rate Schedule
Rick Sutherland
Local reef: 9:00 11:30 2:00 SI at dock
White Sands (4 miles north of San Pedro)
Elbert Greer (Yobubba on scubaboard)
elbertgreer@fastmail.fm
2008 list: by peter of ProTeck
Patojo's Scuba Center | Dive Resort Reviews | Belize | Undercurrent
Action Divers - Portofino Beach Resort (6.5 miles north)
Reef, Hol Chan/Shark, Mex Rocks, Mata Cut, Cypress Garden. 9:00 1:00 no prices.
Chuck and Robbie’s - (San Pedro North )
CHUCK & ROBBIE'S SCUBA DIVING+INSTRUCTION 9:00 2:00
Discover 150, Scuba 375, OW 400, OW referral 275
Ambergris Divers (San Pedro south of ferry) ambergrisdivers.com/
Premier Divers (San Pedro South)
www.premierdivers.com
Dive pool. 1 tank 80, Night 80, Snorkel 64, Discover 180 all included.
Pro Dive (San Pedro South)
Belize Pro Dive Center | Scuba Diving, Snorkeling, PADI Courses, Blue Hole, Barrier Reef, Belize
1 tank 45 2 tank 75 Night 60
Turneffe 3 tank 235
Scuba School Belize (0.5 miles South)
www.scubaschoolbelize.com/
Hugh Parkey's (defunct? San Pedro)
www.hpbelizeadventures.com
Ecologic Divers ecologicdivers.com (defunct?)
Amigos del Mar
http://amigosdivebelize.com/rates.html IBM of Belize Diving
Local 4 divers, atol 10 divers
Patojo’s
http://ambergriscaye.com/patojos/
Belize Academy of Diving - up north
Belize Diving Adventures - S.P north husband an wife, padi staff instructors
Bottom Time
Aqua Scuba (was as Aqua Dives??)
Home
Caye Caulker
Go Caye Caulker.Com - Caye Caulker, Belize - Go Caye Caulker
Belize Diving Services (BDS)
Belize Diving Services - Belize Scuba Diving - Great Blue Hole
technical dive training, and sidemount, might be good for teaching as well.