Why are students with special needs / (developmental) disabilities the oldest high school students in HS?
Students in special education are permitted to go to school until their 22nd birthday. Some of these students may have repeated a grade and that might explain why they are older. Some are involved in work/study programs and so it takes them longer to complete school because they may only be attending school part of the day. Some may go to vocational/technical schools and it may take them longer to master the skills they need to obtain a job.