A tool, for dressing both the inside and outside working surfaces of cup-shaped abrasive wheels used for grinding gears, is disclosed along with methods and apparatus for using the tool. The working portion of the dressing tool has a cylindrical shape with an outside surface parallel to its axis of rotation and a top surface extending radially, to the axis of rotation. The apparatus orients the tool relative to the grinding wheel so that only the outer cylindrical surface of the tool is used to dress the inside working surface of the grinding wheel, while only the top surface of the tool is used to dress the outside working surface of the wheel. Formulas are provided for calculating the optimum radius of the cylindrical surface of the tool for providing substantially equal effective relative curvatures between the tool and each of the respective sides of the grinding wheel, thereby resulting in similar grinding characteristics being dressed into both the inside and outside working surfaces of the grinding wheel.