Also since freshman tend to not have as high of a chance of making their high school's team, allowing 5 9th grader's in Div B lets them still compete.
I doubt that plays a big part. It's significantly easier for a freshman to be as good as someone a few years older than for a 6th grader.
True, but its still very difficult to make a 15 person team of upperclassmen in who have all taken or are taking AP science classes, when the highest science class a freshman would generally be in is Chemistry 1.
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