Was he refusing to GO to school? That's easily solved- physically pick him up and put in car. Or look at why- for example I didn't want to go to school for a few months in year 6 and I never told my mum it was because two older girls were picking on me.

Sounds like he's refusing to get himself ready! That ones easier.. Here's a few that friends do/I do, as food for thought.

One friends dresses her 4 boys in their school clothes/daycare clothes the night before, all he has to do in morning is roll out of bed (that one doesn't work for me as I let DD wear unmarked school dresses twice before washing so feels a bit eww)

Keep school shoes and hairbrush/hair ties on brush handle in car, make them remove shoes before they get out in afternoon, don't do the 'key dance' by the front door, hand them socks with their lunch boxes (we do this, finding matching socks and locating shoes is half the battle and she has FORGOTTEN to put shoes on 4 times in 2 years- she's realised AT school drop off point)

When I stress DD about her time management, she loses it and will just lock herself in her room or cry on the couch. She's only 7!! School mornings are a horrible childhood memory for me and when I realised I was doing to her what my (slightly insane) mother did to me, it changed everything! I realised.. how dare I think of my own child as lazy, even in the depths of my darkest morning moments! She proactively brought our dry washing off the line yesterday and put in laundry. how many 7yr olds do THAT to help mummy?
Our kids were born with parents doing everything for them.. Honestly, without us teaching them super easy ways to do it alone, giving them incentives, and helping if needed, why SHOULD that change? They don't have our perspective on the whole thing.

So halfway thru year 1 I changed our system. Her clothing system is basic- 5 drawers labelled undies, school, pants, etc. Nothing is folded as she chucks clothes in drawers herself- but she knows where it all is. Her weekly hanging rack has about ten outfits including school clothes that she can change into etc whenever she needs to- no cupboard clothes get touched except when I decide to dress her up- out of sight out of mind! Her room has been 100 times tidier (helps their morning state of mind from being overwhelmed), and I also implemented the rule that as soon as she is dressed and has breakfast in front of her, she can do whatever the hell she likes until I'm ready to leave, as long as she doesn't bring out toys or craft. Normally that is playing on ipod touch or watching ABC3. I rush past, throw her lunchbox and socks at her, she rolls her eyes, gets her school bag and follows me to the car. It's funny how I used to blame her but I now realise how often it's ME running late and wasting time.

Also I know your son getting overwhelmed or annoyed like mine does when we clash MAY not be the issue- but my point is, by dramatically changing the routine and keeping it calmer, it changed her whole mindset. I'm the only one that can head off morning conflict! Your household is in a cycle and changing that can sometimes make a world of difference, especially if you explain to them what you're trying to achieve and if they think it will help.

Oh and lastly I've found if she is in a tv/breakfast/couch/toilet daze and I need her to get moving, (yes, she zones out on toilet playing with the rolls and making mirror faces) I just threaten to run late to her next after school activity. Honestly, sometimes they just need a really happy upbeat-voiced loose threat along with a physical pat or touch on the back/arm/shoulder to crack them out of it! I stroke her cheek or hair which she hates, and she leaps up and runs off. I have a floaty day dreamer