Bowel training generally takes longer than bladder training. Be sure your son is learning to urinate in the potty while sitting down. Although boys can be trained to urinate standing up, this should only be attempted after bowel control is established. Standing up to urinate may cause them to forget to have BMs sitting down. When your son goes in his diaper, take him to the potty and empty the diaper there with neutral words of encouragement. Although you should never keep children in dirty diapers as punishment because it creates a confusing message of what is truly desired, you also do not need to drop everything as soon as he comes asking to be changed. Tell him you will first finish whatever you are doing and then change it. These times are not meant to be pleasurable or fun, but you should also try not to sound disapproving.
Most importantly, if frustration is setting in for you or him, it may be best to take a break from training for a while. Do not expect perfection -- three steps forward, one step back, is the norm. An important aspect of training is a relaxed, casual attitude with a sense of humor. Avoid pressure, coercion (being too forceful), or punishment at all costs. For your son to succeed, the timing must be right.
Hank Bernstein Children's Hospital