Switching the retractor on boosters

I know that the current party line is NOT to switch the retractor and lock the seatbelt for a booster rider. And my understanding is that it increases the risk of submarining.

My son's pediatrician asked about boosters at our recent well-child visit. He said that he recommends locking the belt so that kids don't move around too much. I (hopefully diplomatically) educated him that locking the belt for a booster is not currently recommended, that you want the torso to be able to move forward some before the emergency locking retractor engages. And that if a kid can't sit still in a booster, that they really need to be in a harnessed carseat. He was surprised to hear this and thanked me for the update.

He wonders, though, whether having a locked belt might be the lesser of two evils vs. having a child leaning down to the floor to pick something up. He feels like there are many patients in his practice where he struggles to have kids use a booster after age 8, or use a bike helmet, and that there's no way that he could convince a lot of parents to buy a harnessed seat for a big kid.

I found this, as "official" confirmation of the recommendation not to switch the retractor, and I'll share it with him. http://cpsboard.org/cps/wp-content/uploads/2014/06/TechUpdateSUMMER2014_FINAL.pdf

Thoughts?

In addition to not being recommended it is not allowed by many boosters and also many vehicles. (Toyota for one forbids it. I know other brands do too.)

While I take his point, I'd encourage him to educate families about the existence of higher weight and height harnessing seats and the need to teach and enforce proper booster use.

Sometimes there's no choice but to send a 3 or 4 year old out in a booster and locking the belt is the lesser evil. Sometimes it's a useful training tool. Sometimes you have a large child with a neurological obstacle to sitting properly and a family without means to get a bigger harness. There are times you have to. But as a general practice it should not be recommended. In fact, I'd encourage him to send parents to a CPST local to them rather than give specific advice. That way he's not relying on outdated info or trying to keep up. (Or if he has a passion he could get certified!)