Hi – not sure if other sources of training help but I found ADHD training and suggestions from Witherslack helpful: https://pages.witherslackgroup.co.uk/adhd-conference-2022 (free online)
I haven’t suggestions for evidence directly describing what works will underpin the time needed for support or adaptations.
Also ADHD is generic as a term does the pupil have more detail on the type of ADHD? e.g. impulsive or inattentive or combined. It sounds like they may need a structure or framework, including visual or auditory support and some motivational element, to maintain attention and resume attention within tasks rather than stop, refresh and return. Good luck