To think that frequently telling a 3 yo that he "needs to be a good boy" doesn't really work and often has the opposite effect?

[Anothercuppatea]

That's it really

It depends what happns next surely? If he is only told to be a good boy and there are no consequences that depend on whether or not he obeys then you are right. If there is a consequence (yes you can have a ride on the fire-engine-machine at the checkouts because you were a good boy going round the supermarket well done/no you cannot watch one more Abney & Teal because you were not a good boy when I told you to help clear up the toys) then it can work - but only if the consequences are very quick and directly related - a treat awarded or witheld in the evening because of behaviour in the morning will not make any difference.

Does he understand what he needs to do to be "good"? Seems a little vague to me.

I just think a more specific request is required. Like "you need to stay by mummy and not run off" "you need to sit nicely at table" "you need to play nicely and share your toys"
Just saying "be a good boy" isnt that clear to them. And implies you expect them to be bad.

Depends on the child. DS understands the concept of being a good boy so is is fine when he wants to be

I think it does help if you give them some sort of context though "Will you be a good boy and help mummy put the trains away?" type thing

"Being a good boy" doesn't mean anything to a 3 year old. He needs more specific directions for it to make sense.

I agree. I only say "good boy" or similar when he has complied with a specific request.

I hope you sat down and imparted your wisdom with her.

I keep biting my Tongue, cos it's not my place to criticise.