Could you define being a good listener? I mean, I know what it means in general, but different people measure a good or bad listener in different ways.
Transition can always be difficult. Also the difference between a 2 and 3 yr. old class can be pretty big. The class is larger with more students, there are more activities and centers offered, more is done in a day, and more is expected as far as behavior, obedience, and self control are concerened.
It's important to remember that 3 years old is just 2 years old plus one day. In other words, it's a chronological number. There are certain milestones for your son to meet that are important as far as language and motor skills and such, but others take more time and don't magically appear on the day a child turns 3 or even a few months after.
I think it is probably the big change and that means consistency with you at home is the key. Set rules, guidelines and consequences (BOTH good and bad) for behavior and just stick with them. If he does well he gets more play time outside, or game time, etc. If he doesn't do well he gets less. That way he can see the cause and effect. It will get better, I promise.