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I do, at our local high school, and I usually invigilate for special needs candidates eg those who may have a reader or a scribe, or require extra time (NB the readers/scribes are usually TAs who work with the student regularly). Check the websites of your local high schools/colleges, or see adverts in local press for vacancies (or maybe even make a direct approach to schools/colleges - most have a pool of invigilators). You should be aware that the work is very part time, I usually only do a few hours a week during exam seasons - for example I am invigilating mock GCSEs at the moment, will do a few GCSE modules in January and may be March, but the main exam season is obviously May/June.
I prefer individual invigilation with special needs students to invigilating in large exam halls.
Universities recruit for full-time support workers for disabled students in the run-up to the start of the academic year in October - keep an eye on their websites/job ads in your local paper at this time.
You probably wouldn't get work as a scribe, that is done by TAs. Schools do employ exam invigilators, but as the poster above said, its usually only when they have too many exams to cover with their permanent staff, so not that many hours.