On balance beams and 2X4's. Most hitting coaches I know don't use these and they went our of favor around 6 years ago. I would not recommend this drill as you can not get to heel plant and generate the angular ground forces required for rotation because the board is not wide enough. Additionally the back foot can not roll in towards the inside edge of the foot and then up because there is not enough board to land on.
you want them to stride forward use a 4 X 4 not a 2 X 4 and lay it on the ground in a straight line, we term this straight line as a line of force as we always want them striding straight ahead and not at an extreme angle. Use the 4 X 4 so they kick it versus the 2 X 4 which they can trip on or step on so they do not twist their ankle. If the are striding towards the plate place it on the toe side and if they are striding away on the heel side.
you want them to stride forward use a 4 X 4 not a 2 X 4 and lay it on the ground in a straight line, we term this straight line as a line of force as we always want them striding straight ahead and not at an extreme angle. Use the 4 X 4 so they kick it versus the 2 X 4 which they can trip on or step on so they do not twist their ankle. If the are striding towards the plate place it on the toe side and if they are striding away on the heel side.