Final answer:
A power wheelchair is the most beneficial mobility equipment for a fourth-grade student with muscular dystrophy to independently participate in outdoor games at the same rate as peers.
Step-by-step explanation:
For a fourth-grade student with muscular dystrophy who uses a posterior pediatric walker, independence in outdoor games is a key goal. Considering the need for close supervision and the student's ability to engage at the same rate as peers, a power wheelchair would likely be the most beneficial mobility equipment. This type of wheelchair provides the user with greater independence and maneuverability, enabling them to participate more actively in dynamic outdoor activities without expending excessive energy or requiring constant physical support.