i have had 2 chronic school refuses here!! It is so hard and so emotional- both my twins are so it was double trouble ganging up on me!!
We are still late nearly everyday as they are both still so hard to get to school
What worked for me when they were your child'd age :
- Get the school on board- know what is going on- our principal was awesome and she would sometimes come out to the car and help me get them into school some days.
- I got my DD teacher to assign her a job that had to be done each day before school, so she had to get there before the bell to do that job so that got her there on time
- arrange a play date before school with some of the other kids mums so that they wanted to get there early to have a play
-bribery/rewards when they go so many mornings getting to school without fuss
-counselling to find out the real reason why they are school refusing- both my twins had different reasons- both were valid. It got so bad the reason that my DD was refusing to go to school, that we actually in the end swapped schools. She still even to this day gets some anxiety , but it is alot better and episodes are more in waves now rather than all the time
-step at a time. The main goal is to get to school but break it down into smaller goals. In other words "I'm not asking you to go to school, I am asking you to get dressed/eat breakfast/put your shoes on," etc . One baby step at a time. Something the whole routine is so overwhelming.
-a treat- and it doesnt have to be food- in their bag that they can look at or have when they get to school! Stickers or a new eraser/pencils worked well for us.
-lots of rescue remedy/crystals to hold/little toy/security object have been used for us

The main thing is not to do it alone- you cant- you need back up and have a plan to follow when they do refuse. Also take the emotion out of the whole situation. That way the emotional blackmail doesnt work. Also blaming someone else for the reason they have to go to school- ie authorities fault you have to lol .
Just try and keep one step ahead of their objections and have a plan if they try and deviate from it
HTH and good luck and hang in there !!!