Probably mostly echoing others, but this is what I would do:
Strap him in buggy for journey to school. Look him in the eye and say gently "I know you don't want to be in the buggy, but we need to be quick. You can ride your scooter on the way home." Yes, he'll kick off but at least you've shown empathy whilst still keeping to a necessary restriction.
Ignore the screaming all the way to school - believe me, I know how incredibly angry it can make you feel, but you're doing the right thing, so take deep breaths. The more you practise calmness whilst they are going mental, the easier it becomes.
Let him scoot home as promised, that way he will get better and faster.
Do not offer bribes of food or technology. You need to get your child to learn to behave when you are making a reasonable request, because they understand the importance of that request, and because they want to please you. Not because they think they will get chocolate or screen time.
Ignore other parents looking serene - if you happen to be on my school run, I can assure you that I am a swan (calm on surface, flapping madly underneath). Also, some kids are more headstrong than others - not necessarily a bad thing once they get a bit older and can channel their determination appropriately.