L.A.
My son just turned 4, he stopped taking naps at about 2 1/2 years. When we started having problems with him sleeping at night I took a step back and looked at what we were feeding him and what his activities were during the day. I noticed I was feeding him too much sugary foods and empty starches that had him wired for the day. Since then he only drinks water(no juice). we began adding more fresh veggies and fruit, less starches and more protein, etc. Also we started getting outside more and going for walks or just playing soccer or something like that. It not only dramatically changed his sleeping habits but his behavior as well. He still doesn't take naps (even now at pre-k) but he would sleep all night.
At Pre-K they were giving him a small cup of jucie at snack and we were fighting him to go to bed around 10-10:30 the first week. The second week I told them to NOT give him juice but water instead, he is now falling asleep on his own at 7:30-8 at night.
I know for some kids juice and sugars don't make a difference, but for some, like my guy, a small cup of juice will keep him up for hours.