A couple of points:
1. Was there a medic at scene at the pool to clear c-spine? How do you know that the kid was "fine" without x-ray glasses?
2. Minors or people under the influence are not legally competent to refuse care. Period.
3. If someone doesn't want to be backboarded, even when you ask nicely and explain why you are doing it (and they are not competent to make care decisions on their own i.e. intox or minor) then don't be afraid to man up and call law in or use restraints. If someone is altered I often use restraints and it's my butt on the line if I didn't c-spine them when they needed it.
Sometimes you just need to assert your authority to get it done.
B)