Physicists have found that peeing standing up significantly increases the velocity of the stream and potential for backsplash, amounting to less hygienic, more bacteria-filled bathrooms. So if dads aren't going to pee sitting down for their prostates, they can do it for their partners.
Other tips and tricks for transitioning your son to standing and helping with aim: make a game out of it and throw something like cheerios into the toilet to act as a target, add food coloring to the toilet water and let him watch how it changes colors as he pees, let him practice in a designated spot outside with