it went up to hb0.4m, but not enough.
If you want to speed his learning of surfing:
This is what he can do beside you while your are SUPing in flat water...
(1) learn to paddle:
(2) learn to rest, sitting on his board, as breaks while paddling.
http://www.surfing-waves.com/sittingboard.htm
So next time there are waves he can focus on standing up and less on balance:
The smaller the board (less weight) the safer it is, as the board is a piece of furniture next to you in semi controllable conditions.
Surfboard size, just a head over his height:
This is by experience, I am not an instructor, same as any windsurfer giving pointers on windsurfing.