There's a European study that suggests that a good high back booster improves safety by 70% compared to backless boosters in side impact crashes. Comparatively, there was a CHOP study that didn't show a difference in real-life crashes BUT that study failed to control for a LOT of confounds, like proper use and whether the boosters provided good belt fit.
Of course the ultimate goal of the booster is a correct belt fit but I do recommend using the high back for children who still fit in it, due to the potential head protection in side impact crashes, the reminder to sit correctly, and the added support for napping.
Quote:
Originally Posted by
TiredX2 
Is there a safety reason to use a high back booster over a low back? In one of our cars, the kids actually preferred the fit and feel of the seat/belt without the back.
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