Why Will He Listen to Me but Not His Birth Father, Who I am Marrying?

That's pretty much it. I'm a single mom, engaged to be married to a man who has a 25 year old son, a 24 year old daughter, and a 10 year old son.

The 10 year old is extremely clingy with his dad, and honestly, acts like a 4 year old. Which is ironic, because my 14 year old daughter, acts more like she's 18 maturity-wise. She's researching colleges, focused in school, and enjoys the martial arts courses she and her future step-brother take.

The 10 year old, in the past week, has been late getting back from his playtime across the street twice, was banging on the outside of the house, leaves dirty socks all over the house, and dirty dishes in the family room. He has been paddled in school, he either can't or won't focus in school, and skips karate classes after I drop them off.


When his dad asks him to clean things up, there are never any consequences. His room is a complete disaster area, and a month ago, Dad said, "I want this done by Friday." The son said, "ok." and well, here we are a month later and it's still a complete mess.

There are no consequences issued at the house for anything that he does, when he skipped the karate classes he was told, "Either you do all of them, or you're done." There were no consequences whatsoever for his paddling at school, no discipline in regards to his disrespectful speech toward his father, and nothing done when he almost failed a grade in school.

Whenever I bring up that there is a behavioral issue that needs to be addressed, I feel like I'm just being blown off.

Here's the kicker...the child will listen to me. He won't listen to his dad, but he listens to me.
Any idea how we can get this child to respect and listen to his father more often?