What does "substantial limitation" mean?

An impairment in and of itself is not a disability. The impairment must "substantially limit" one or more major life activities in order to be considered a disability under Section 504.  Substantial limitation means an important and material limitation and must be made on a case-by-case basis with respect to each individual student. Substantial limitation in a major life activity must be measured against most people (or the average student) in the general population.  Furthermore, this analysis must be done without consideration of the benefits of mitigating measures, such as medication; medical supplies, equipment or appliances; low-vision devices (which do not include ordinary eyeglasses or contact lenses); prosthetics (including limbs and devices); hearing aids and cochlear implants or other implantable hearing devices; mobility devices; oxygen therapy equipment and supplies; use of assistive technology; reasonable accommodations or auxiliary aids or services; and learned behavioral or adaptive neurological modifications.