One of the diagnostic criteria is that the symptoms are evidence across settings.
School is the setting that a student spends the most time outside of the home.
It is possible for home schooling, but you have the challenge of a limited amount of rater responses in fewer settings.
To get around this, you have a few options.
1 – Evaluator observes outside of the home.
2 – Are their other potential rating scale respondents? A Sunday School teacher? A karate instructor? Coach?