Who does the classifying?

Each sport's International Sport Federation regulates classification for its sport. Athletes are assessed by a panel of accredited classifiers trained by the federation, typically two or more classifiers, guided by published sport-specific criteria.

Panels are made up of classifiers certified by the relevant federation in one impairment group: intellectual, physical or vision.

Sources: https://paralympic.ca/sports/classification/ and https://www.paralympic.org/classification