If intelligence is distributed on a bell curve there are going to be some that can't graduate no matter how hard they work, and some more that can only graduate with a lot of hard work. Then throw in some more people that have some difficult life circumstances: parents dying, depression or other health issues, drug or alcohol problems, etc.
>>confid+(OP)
This number is including the fact that we already lower standards for those on the left side of the bell curve. It's entirely the difficult life situations at play.
>>confid+(OP)
In my experience they just stop attending, not hit a class they can't pass. There is no standard of achievement required to graduate high school besides participation.