Absolutely needs a longer, more explosive stride that begins with a stronger leg lift. I know the towel drill is an old cliche, but I still use it when teaching for kids who like to just open their hips and plant their foot for a weak, short stride. The Tom House rule is to have the player go through his motion, mark where his front font is landing, and then step back five foot-lengths as a starting point. Kneel down and put your glove out at the pitchers' waist level, and instruct him to snap the towel and hit the mitt.
I tell them to bring their front hip at my mitt and really feel themselves accelerating down the slope. Slowly give them a farther target to hit with the towel to lengthen that stride. Make sure they aren't just jumping down the mound (younger kids like to do this), and that the drive is coming from staying closed longer and creating force with the back leg.
Mr. Peterson here has to get more explosive down the mound, and I think this would help.