@FedNlanders some schools mark very harshly and have excessively high grade boundaries - at our school you need 90% in maths to get A, although last time there was a real exam, an A was about 72%, so they might be pessimistic grades.
You need to talk to school, but would he be willing to re-do Y12? It has been such a disrupted year, so repeating the year to consolidate could work for him.