If you are gonna do it, you have to be consistant and make sure the nursery school is on the same page as you as far as the potty training. Often boys take longer to "get" the whole going to the potty thing as it is a different sensation than what we girls have.
I know several boys that were firstborn children that didn't 'get' the whole idea until their younger brother (12 or 18 months younger than them) started potty training on their own while their mom was trying hard with the eldest... then it just 'clicked'.
My brother took forever, and as a contrast from what I am hearing from my mother in law, my DH trained and totally got the concept at a very early age because he wanted to go to kindergarten (which starts at 3 here). She said he hated being wet and gave up the diapers on his own, and threw a fit when they took a long trip to switzerland and she had to put him back in diapers because they couldn't stop along the way for potty breaks (not many rest stops 24 years ago). He cried for a couple of hours until they could stop by the side of the road and hide him behind a tree.
I do remember vaguely when my mom was trying to train my sister, and the biggest thing at night was making sure she went before she slept and had nothing to drink an hour prior to going to bed, and walking her a couple of hours into sleep to the potty to go again before my parents went to bed. During the day she had her in regular panties and just kept her in the room with her and asked all the time if she had to go, and took her at regular intervals to the restroom.
If you really watch them, you can read their body language before they have figured out they need to go to the potty. They start giving subtle hints.
Some friends of mine kept a potty chair in the room they were in, just in case they couldn't run to the restroom fast enough while training their child... seems like a smart idea to me, considering they have wood flooring!!
Each child is different, and some kids take as long as almost 4 or almost 5 to totally get the whole idea of potty training. Some get it as early as 18 months.