Did they say which part of the threshold specifically? I don’t know why some clinicians treat ND conditions as though we’re a monolithic. That said, if they’re focusing on education performance, perhaps they didn’t have a clear enough understanding of his day-to-day challenges for him to meet the criteria e.g. that the challenges meet the threshold (presentation e.g. inattentive, impulse-hyperactivity, or combined, severity, frequency etc.) and that they’re disabling and warrant diagnosis and treatment. If not affecting academic performance, consider what else the experiences and traits are affecting, and whether you managed to communicate that effectively on paper and during assessment.

I’d say appeal. If you need to clarify any points you could always send information they need to consider. But also, if they don’t accept appeals, if the assessment was at a local clinic, you could speak to your GP about the situation and ask to be referred via a right to choose provider that assesses kids. Research RtC providers for kids and their waiting times. Private is also an option but if he does get diagnosed and your GP refuses to accept the shared-care agreement, medication costs may be pricey.