"My husband and I have 2 kids, ages 4 years and 6 months. The 4 year old has followed fairly well along with your suggested timeline for adjusting to his sister, and I am currently seeing his behavior as much better at home and feeling much more connected to him than I did just after the birth. His behavior at school, though, is up and down. I work part time and he is at preschool about 8 hours a day.
My husband is a firm believer in spanking and I am not. We have talked about this quite a lot, and are not having luck coming to a compromise. My husband was spanked, but not much because he witnessed his older brother getting spanked often, and that worked as a deterrent for my husband. I'm not a believer in spanking and neither was my mother, I was raised (33 years ago) with playful respectful parenting and positive discipline. My mother never read a book about parenting, she just followed her heart and that's what happened. My mother is my parenting model. I'm an only child, and one of my husband's arguments is that he thinks I just don't know anything about parenting boys. I personally think that gender is irrelevant, we need to find approaches that work for our son, but not based on his being a boy, based on his being an individual.
My husband's approach to parenting is very authoritative, he thinks we (as parents) should be in charge, and our kids should 'do as they're told' promptly when commanded. He has a lot of rules, and generally forbids much more behavior than I do.
So, my son's behavior needs to improve, he's very high energy and rough, and we have a hard time getting him to calm down and respect the personal space of others, especially me. He is very rough with his toys. He also has this problem at school as well as choosing not to follow directions and generally disrupting the classroom. I think his behavior is fairly age appropriate, but it needs to be toned down. My husband thinks he needs more spankings.
I suspect the differences in my husbands and my parenting approaches are doing my son no favors, but I don't know what to change to get us closer to agreement on how to handle my son's actions.
My son has been at his school for over a year. He has been in full time daycare for 3 years. This type of behavior started around the time he turned 3 (a year ago) and has been worse the past 8 months. Other than the arrival of his sister, 6 months ago, nothing major about his life has changed recently."
This is a tough question for me to answer, because I honestly don't really know how a couple can bridge two huge differences of conviction (because it does sound like both of you are truly convinced of the correctness of your approaches). And it's very hard for me to see your husband's side in all of this, because I'm an anti-spanker (although I have gotten out of control and smacked and felt like the lowliest worm in the world, and hey, it didn't even work, surprise of surprises) and think that it can be especially damaging for boys to be disciplined with violence. (Not that it's not damaging to girls, but I think it's damaging in a different way. That would make an interesting discussion for another day.)
So I really don't have any advice on how to make a compromise. In your situation I would try to convince my husband that spanking is counter-productive. The article "Ten Reasons Not to Hit Your Kids" is excellent, and there are great links at the bottom of that article.
I'd also talk to the teachers at his school to see if you can enlist them to talk to the two of you together about better strategies for disciplining your son. (If the teachers at school don't spank the kids there, then that means that they have effective alternative strategies to teach you. I feel like most of us vastly underuse the excellent brains and extensive experience of our kids' preschool teachers.) To me, your son's behavior sounds absolutely normal, especially considering that it all escalated right before having your daughter. ("High energy and rough": check.) Older siblings act up for a long, long time when a baby sibling comes into the house, and it's just not reasonable to expect that they'll be "used to the baby" in a couple of months and will stop acting out. IME, it really took a full year before my older son got his feet back under him again after our younger one was born. In addition, 3 is a tough age, and kids are just starting to approach the border of being able to control their own actions. It can be extremely hard for them to navigate boundaries and control and language and physicality.
One of the strategies you may end up using is physical guidance. Not violence or pain (hitting, smacking, etc.), but guidance. My older son needed/needs this. He has never been able to stop himself from doing something when he hears a verbal command. If I needed him to put down a toy, I had to walk over to him and put my hand over his and help him release the toy. Back when he was a toddler pulling our cat's fur, I'd have to walk over and help him release the cat's fur from his hands. If it was time to leave the playground, I'd have to put my hands on him and help him wave to say goodbye to the park, then help him walk out of the playground. He was also one who needed to be hugged during a tantrum. It's like he needs the physical help to make the neurokinetic connections. I think there are some kids who are more physical who just don't respond to other forms of guidance, but parents often don't think of guiding them physically because they didn't have that example. (FWIW, at the age of 4.9, my son is doing really well at controlling his own actions, but he still seems to engage in selective listening more than I'd like!)
My suspicion is that I've answered your question the way you wanted me to, by giving you resources to help convince your husband that your approach is going to work better in the long run. But it's possible that you actually do want to be able to reach a compromise, in which case I'm going to have to go to the readers. Have any of you bridged a huge gap in approaches to parenting? How did you do it?