We had been trying to potty train Declan while keeping him in diapers for at least 6 months with little to no success. We used a variety of techniques I'll list below but ultimately what worked was to just switch him to underwear (and pullups at night) and in essence, let him learn from his mistakes. It's a bit messy but it only took 4 days and turned out to be much easier than I imagined.

Method... it's hard to say if all these are required:

1. Keep positive. Celebrate successes! Don't punish or associate anything negative with "accidents".
2. For motivation, we created a sticker based chart (I tried, I went, I put the seat down, I wiped, I flushed, I washed my hands) where he got a sticker for each task he accomplished and got to wear a sticker too. We also floated the promise of "Big Boy Diego Underwear" once he filled the "I Went" section (20 boxes) but ultimately just went and bought the underwear and put him in it.
3. There wasn't really any indicatorNo acknoledgement that he had to go, no willingness to try, no success when he did try, ...
4. On Thursday, we did a complete changeover as friends had advised. He wore underwear during the day and pullups at night. Advice from friends, "once you start, don't turn back, no more diapers once you make the switch.". We didn't, it worked.