I'm in agreement with Monster on this thread. My partner of 12 years and I had to reach an agreement on how to raise MY 2 children, including one who did not have a father in his life. What worked best was for us was for my partner to support ME as I set boundaries and disciplined MY children. He is my partner, not their father.
That said, does your stepson understand the concept of consequences? If the clothes are not picked up, the PS3 does not get played (remove it from the house, if necessary). I have a key lock on my bedroom to enable this sort of consequence. If schoolwork is done, then you can watch TV.
As long as certain chores are complete, my kids can set in front of the TV in their jammies all weekend as far as I am concerned. But they have to earn that privilege. I have parental controls on my TV and Internet and have no problem removing doors, tv's, computers, phones, etc. to enforce loss of privilege. They go into an offsite storage unit.
As far as school is concerned, my son, who is very very bright, was bored to tears by normal school curriculum. He began failing everything, simply because he couldn't be bothered to do what he considered "that boring crap". The school transferred him to another school that has more hands on type curriculum and my son blossomed! Instead of reading a textbook about physics, they built a rocket and shot it off, for example. My daughter, who is ODD, we got into a charter school that lets kids go at their own pace, online. Took extra time for her to get through school, but she did it. The ODD about killed me, but consistency and firm consequences worked best to help her. Also, lots and lots of love. I don't believe in spanking/hitting, and they were raised without it.
Very successfully, I might add. Of course, the 9 yr old (our child) still has a ways to go
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