Forget M&M's or any food as a "reward" for using the toilet. That never worked for Matthew anyway.
Unless his bladder has reached or exceeded maximum capacity, Matthew will sit on the toilet and hold... hold...hold... and nonchalantly act like he doesn't need to go. BUT show him your armpit and say you'll let him tickle your armpit after he pees. And just like turning on a faucet, he wills himself to pee. Several times while he's going, as crazy as it seems, he'll stop peeing midstream and want to tickle your armpit. Saying he can AFTER he's done, he restarts the flow instantly.
As soon as he's done, he gets his "armpit reward" and many chuckles out of him and us. I'm not sure which he finds more hilarious - the fact that he gets to tickle our armpits or that he's secretly got us under his "potty control".
Does He Initiate?
Usually not. But there are a few times he has. He'll either come find me and say "I need to go potty" and lead me to the bathroom with him hand-in-hand. Sometimes, his pants and underwear are still dry. Other times, he had already leaked into them. He knows very well when his pants are wet or dry. And there were a few times in the past 3 days when he went to the bathroom himself and just needed my help getting dry pants and underwear from the closet.
Bigger bladder? Better Control?
I'm not sure. He may have a bigger bladder. After all, he has grown some.
Seeing how he can stop the flow midstream, I would think he had better control. But why the leaks/ accidents? Some days he can hold it for an hour. Some days he has held it and stayed totally dry for 2 hours.
We have had some success using include clapping, lots of praise and cheers, bringing a small toy to the bathroom, allowing him to read a book while on the toilet, and playing on my iPhone while on the toilet. Some worked better than others, depending on his mood. And some were effective only for a couple weeks.
The most effective strategy we've tried is using a kitchen timer as an audible cue that it was time to go. It worked like a charm for a whole month and a half. No resistance whatsoever from him. Then it got to be less effective. I must have jinxed it by blogging about it. He actually still responds to the timer going off and knows it's "potty time!" but he needs more convincing these days. So we still use the timer despite the muted effectiveness.
Another effective strategy that we still use is giving him a short sequence of activities he can expect after going potty. For example, "go potty, get dressed, wash hands, listen to music." Or "go potty, wash hands, blow bubbles." The key is to know what HE wants to do in order to truly motivate him to get through the pottying process without spacing out, without a tantrum, and with as little help as possible.
By the way, this is our 10th month into potty training.