I have a teacher friend.
He told me the school gets a certain amount of money per student based on the percentage on attendees per day.
If attendance is way down on a day they actually go out on the street and drag people in to fill the roster.
They also get something like $400 per 'handicapped' child.
ADHD is considered a handicap.
$$$$$
It is hard to get special ed designation, and the districts do not get enough money for special ed services, so they like to refuse them to qualified kids like my daughter (with brain damage).
In California, the amount of money the school gets is based on attendance. One school in San Jose, the principal asked parents to take their sick kids to school so they could be counted as being at school, and then pull the kids out sick.