For students and families:
Exam access arrangements refer to the type of help which students may benefit from in exams, such as extra time. Such arrangements must reflect students' normal way of working and therefore schools and colleges take the lead in determining if any help is needed. If you think your chld needs help in exams, you must talk to the SENCo in the first instance.
In the vast majority of cases for GCSE and A' level exams, short assessments are handled in-house from year 9 onwards. If this is not possible, the school is likely to have an established working relationship with external educational psychologists and specialist teacher assessors, and can advise families who to approach whilst following the regulations set by JCQ (Joint Council for Qualifications). However, I'm always happy to forge new links with schools/colleges if they'd like to work with me and use the scores from my reports.
I often see candidates taking professional exams, such as the ICAEW, UK legal qualifications, US state bar exams, etc. Clients are advised to check with the professional body about exactly what evidence is needed (i.e. a full diagnostic assessment or purely for exam access arrangements) and whether additional paperwork needs to be completed for which there may be an additional cost.