I think very few heads ever used a run upwhen caning a boys bottom. The only time this may have been done was if the caning was done in the gym or school hall. Here the boy would here vthe teacher apoproaching, so adding to the suspense before feeling the terrible pain. Even in this cases I should imagine the teacher stopped and took aim at the waiting bottom.
I think the run up is more part of fantasy bthan fact, but may have been used. Firstly, most heads caned in their office and would not have much room to take a run up…..may be one or two paces at the most. Secondly, the most effective caning, the ones that sting the most, is when the cane is whacked right across the boys bottom with it landing flat. This way most flesh is hit and so causes pain right across the target.