I’m going to offer another perspective than the “let him rest and don’t push him” one discussed here.
Our second daughter did this in year 9 in Aus, she was 14. She’s in year 12 now. I’m pretty sure she’s not ND but she was definitely socially anxious. There was no obvious reason for the school refusal but I think a perfect storm of teen issues - braces, acne, social groups moving around, giving up a competitive sport all contributed. She refused to see a psychologist but did see a dermatologist and her skin clearing up helped.
She’s always been a very pretty girl (I’m biased obvs) and the acne in particular was devastating for her self esteem.
What got us through is that she’s inherently very bright, has her mind set on a degree in astrophysics since primary school and essentially liked her school and her teachers. She goes to an academic private school in Australia. We said that if she carried on as she was we’d pull her out and that it was too exhausting for everyone to continue with a daily battle. We removed all unnecessary screen time from her phone and if she was at home we took the tv remotes away while we were working.
One of her year 9 teachers was so gentle and understanding and would let her sit with her in the class at break if it all felt a bit much.
By year 10 she was fine 🤷♀️. New friends, new sport that was very social, focused on school work, no attendance issues, part time job, a few parties and a bit of rebellion but nothing excessive.
She’s now in year 12, a few weeks away from her final school exams, has topped the school in physics and is aiming for high 90s in all her subjects and a particular uni course. There’s still typical teen stuff but nothing out of the ordinary.
ETA : I’m going to add that I felt terrible being as strict as I was about school and tried to make her life easier in small ways, like making sure she always had her preferred lip balm, moisturiser whilst on accutane, kept her room clean (she was happy for me to go in there), made sure clothes were washed and she had preferred foods etc