Step Stool

FIG. 1 is a front, left, and top perspective view of a step stool, showing my new design; FIG. 2 is a rear, right, and bottom perspective view thereof; FIG. 3 is a front view thereof; FIG. 4 is a rear view thereof; FIG. 5 is a left side view thereof; FIG. 6 is a right side view thereof; FIG. 7 is a top plan view thereof; FIG. 8 is a bottom plan view thereof; and, FIG. 9 is a rear, right, and top perspective view thereof, illustrated in a folded configuration. The broken lines in the drawings depict portions of the step stool that form no part of the claimed design.