When evaluating school trolley backpacks, focus on the wheel system, handle mechanism, and fabric durability. Look for silent, 360-degree rotating rubber wheels or sturdy PVC wheels with shock absorption. The telescopic handle should be made of high-grade aluminum alloy to prevent rusting and bending, featuring at least two adjustable height levels. For the main body, water-resistant 600D or 900D Oxford fabric or high-density Nylon is preferred to ensure the contents remain dry and the bag resists tearing under heavy loads.