Lots of coaches teach this. It is particularly prevalent at 10U and 12U, where field players like the 1B sill stand on the base to slow the girl down or stop her from rounding the base properly on balls that look to be hit for extra bases, or the 3B who will block the base path so a girl can't score from second on a single. In fact, off the top of my head I could give you half a dozen names of coaches who teach this and could give you half a dozen more if I thought about it for a few minutes.QUOTE]
I know of coaches in younger divisions that taught this as well. Nothing like teaching kids to play the wrong way! If you are ASA they have changed the rules to discourage this. There used to be a "about to receive" notation in the rule for those blocking a bag or plate. That rule was very subjective and has been removed. Now you cannot stand on or block the base without the ball period. A lot more obstruction calls being made here in so cal.