Potty Training Help???

I lurk on this board often, but I have never posted. 

My son just turned 3. When he first turned 2 he was VERY interested in the potty, wearing big kid pants, etc. So we started potty training last year and it went really well, until we went on vacation. Then he stopped everything and totally reverted back to his old ways, to the point where I have to keep him in diapers when we go out.

Some of my friends think its a behavior issue, since he can use the potty and holds it for long periods of time, but others are saying he's not ready yet and just needs more time.

Here is the situation. If we are home, he will stay dry all day, only because I bring him to the potty regularly. At school, he refuses to use the potty and his teachers don't like to push them if they aren't ready.

I am having a hard time deciding if I think he's ready, because he stays dry all night, he stays dry for hours on end and if we are out, he will wait to go until we get home.

But on the other hand, he never tells me that he needs to go to the potty and seems totally disinterested in everything potty related. He doesn't hide when he needs to poop, having a dirty diaper or training pants on doesn't bother him, and our rewards (we've tried everything from candy to trips to the zoo) and praise seems to fall on deaf ears.

I have no clue what to do. Should I push the issue, or just give him more time??