As an instructor myself I find that many of the "advantaged" kids may take lessons once a week or more. That fact gives them an opportunity to maximize their abibility, BUT, few actually do because they believe that their lessons ARE their practice time for the week. I fight CONSTANTLY to get my students to swing the bat EVERY DAY. I don't ask for hours either. Just give me 5 or 10 good minutes EVERY day and steady improvement will follow. The more GOOD minutes you spend the better you become.
Once a week is certainly better than none and I think things can be accomplished in that time for sure but the advantage only becomes significant with quality practice between lessons. Just like a musical instrument.