FINALLY. I figured it out. I was wracking my brains all weekend long, lost in the details of the science fair, school procedures, blah blah. Then at work today it came to me like a bolt out of the blue.
All the clues are in the behavior of the police and the family. All of us figured out this was being handled strangely. I think I know why. The suspect is the older sibling of a student at the school. That explains everything.
The first clue came from SM who got the word out not to listen to the media - in other words, this is not what it seems to be.
The police refuse to call this an abduction. They also are not interested in sex offenders. They know it was not a stranger who did this. So why not say so? Because he suspect is a minor and is known to the school and the family.
The family does not speak (even though the bio-mom wants to) for the same reason - the suspect is a minor Kyron and one the family know and trust. It is not another student at the school because no other student went missing with Kyron that day.
This minor I believe is a former student and older sibling of a current student for two reasons. (1) He knows the easiest way to help Kyron get out of the school, and (2) he does not look at all out of place in the venue of the science fair even if he is spotted there.
I think the sheriff was in tears today because he knows they are looking for Kyron's body and he knows (as does the family) who did it and why.
I think Kyron planned to go with this older minor; that's why he was waiting by the door after his SM left the school. I also think he believed he was going to be back in time for the talent show. I believe this older minor tricked him into thinking they were leaving and performing some "surprise", maybe for his parents.