"Atta boy!" is just a term used to praise and encourage someone's efforts.
We may use it with pets, boys and girls, especially when they are small and learning to walk and do other things on their own:
We may use it with pets, boys and girls, especially when they are small and learning to walk and do other things on their own:
e.g. "Attaboy, Adam. You can do it! Mama's big boy!"
It is still used when they're a little older and, of course, humorously among adults.