I'm so hearing you sweetie.  Our 5 year old daughter is the same.  Apparently, she is an angel at school, but at home is the most uncooperative little miss. 

Unfortunately, they all go through similar  phases, and we just have to try and keep reinforcing the teachings we put in place before they went to school.

Our daughter has also taken to saying 'but my teacher says.....' as a tool against us, but we are going to nip that one in the bud by talking to her teacher about it.  It seems that Miss 5 expects there to be different rules at home than what are at school.

Our daughter didn't have the benefit of going to daycare before school, so didn't have much social contact.  We think that could be one of the reasons why she is now rebelling at home.

Hang in there, and remember, you are not the only one dealing with the 2 faced monster.  Gone are the days of sweet babiness, look out world, these little beings are here to take over! lol.

He could be over tired. Starting school is a major event and they do tire more easily for the first few months. It could also be that at school, the whole day seems to be about doing as your told and when he gets home, he just wants to let off steam. Its an adjustment stage that takes a bit of time. I'd also make sure he's eating enough, they expend a lot more energy going to school as well as the karate.

I have noticed in my son and some of his friends a real behaviour change - lots more aggression and defiance - at around 4 1/2-5.  I don't know if it is surges of adrenaline or testosterone or what.  However, you tie that in to starting at school, which is also a big change and bingo, you have drama.  How is he dealing with school?  It could be a lot for a sensitive little guy and he may be storing up his frustrations and letting them out at home where he feels safe.  It could also be that mummy is no longer his only boss, but his teacher is, and he is pushing your boundaries to reassure himself that you are still in charge and he is still secure in you (reverse logic but that's what they seem to think).

With my son I have made a huge effort to spend time with him alone and give him the emotional response he needed - he has responded really well and been really loving and happy recently.  However that may be temporary - tomorrow he could be wild again and then we have to assert boundaries and give him somewhere to output his energy.  You take it a day at a time - and pray for patience & forgiveness (which some days I am sadly lacking)!  Good luck!

This is a big change in a child's life and it can be very stressfull.  Have you tried to talk to him to find out why he is yelling and acting the way he is?  Maybe, for him, the karate and school is to much to start at once and thus is feeling overwhelmed.  It could be that he does not know why he is feeling this way, and thus you may need to poke and prod a bit to find out why.  I know for my daughter when she is around alot of people she gets overwhelmed and will shut down and become grumpy.  It's all because she is not used to it and just like an adult can feel overwhelmed, but she does not know that is what is going on.  Try and giving him some alone time when he first comes home, and when he goes to school, do they allow free play in the beging?  That may help him alot.  He just may need to feel secure in his surroundings before interacting with alot of new people.  Same with karate, have him get there a little early to warm up to the place and see if that helps.  And just keep talking, let him know it's ok to not want to interact with others and let him take his time.  He will adjust, but he needs to do it on his own time.  Hope this helps.

Well you could try checking all the possible physical causes; tiredness; constipation; needing to eat more frequently to cover the longer days... And think about any activities he may be missing out on since starting school (less cuddle & chat time?) in case its an emotional need..

Sadly tho, I must say that school changed my daughter's personality too... She became less able to concentrate & less able to complete an activity peacefully; less likely to communicate with me & a bit more irritable.

I have since learned that part of the natural developmental process for children (usually 6 - 9yo) is to place teachers ahead of parents in their estimation. Perhaps thats part of the change too; if he's behaving well for the teacher & not so well for you. 

I just found the whole thing so sad. And seriously questioned (for the first time in my life) the wholesomeness of the school environment for littlies.. I've since concluded that school isn't right for everyone & I applaud those parents who go in for 'home schooling'.

I do hope its something simple like him needing more sleep or more cuddles.. Good luck.

Rosalinda