G.R.
Hi N. - I remember those days & how frustrating they were (my oldest finally was trained by 4yrs old - still had a few accidents and my youngest took a little longer). With my boys they realized that they were "in control" and if they wanted something to go the way they wanted (example: dad taking them to potty), they would hold out until they got what they wanted (it is a power game). For one of my boys he really did not like having wet underwear & the other it did not bother him - just shows us how different kids really are. And yes girls seem to train differently than boys - go figure.
At this age, they are still "learning" how to completely empty their bladder (ok, my now 8yr old is still practicing that - he is too much in a hurry). One of the things that helped me survive was to relax and realize that it can take much longer than "I want" for them to be fully potty trained. We used sticker charts, etc but we also had to wait until they figured out the clues that their bodies gave, we help point out some of them (grabbing, the pee-pee dance, etc). I had my boys in pull-ups when they were at preschool/daycare to help with accidents (plastic pants work too), so it would help encourage them to still use the potty but offered protection. We also set up a schedule: as soon as wake up, after breakfast, upon arriving at school, at recess, lunch, afternoon break, when school gets done, etc. We tweaked that schedule so they were able to use the external clues to "remember" to go on their own without "us" having to be their reminder clock (use help at daycare to continue this schedule). One of the things that our peditrician shared with my older son as he was learning to make sure his bladder was empty (to have less accidents, etc) was to practice counting as fast as he could (1,2,3...to see how high he could get), when he was good at counting numbers then we would count by 2's, 5's, etc. Another idea is to place 5 squares of TP in the toilet & see if he can "sink" them by peeing on them. Hope a few of those ideas that worked for my kids to help empty their bladders will help you too.
One last thought is if your son is going potty every half hour (more than a few dribbles) you can always contact your peditrician and have them run a simple test on his urine (they will give you a special cup). This test can tell how his hydration is, sugars are, etc. This is a standard test as kids get older but is a very good tool to give early warning signs for diabetes, urinary tract infections, etc. More than likely he is just fine & just needs practice emptying his bladder. God Bless & in a few years you will laugh as you remember the perils of potty training.