Here's how it could have happened.
Weeks and days prior to 6/4:
Spend time in the school, check out sight-lines from rooms which overlook the parking lot and the east (unattended, unlocked) entrance. Notice that there is almost no view of area next to east door from any window.
Arrive at the school on several mornings to notice the traffic flow between 8:15-8:30. When do buses arrive; how many walkers and when do they arrive; how many drop-offs and when. School does not open (officially) until 8:35, so that is taken into account.
What is the status of parking places at that time- are there spaces available at that hour which are visible from the school, ideally the gym/cafeteria/auditorium?
6/3
Tell your child you will pick him up at school, near the East door, and do so. The teacher would have had a note or email saying you will do this.
6/4
Make sure your child wears the same (or a duplicate) flashy, memorable tee shirt he had on the previous day.
Arrive at 8:00, select preferred parking place, likely the few spaces in the rear of the school. (Should have been using that place from time to time when at the school.) Think of a logical reason to use that space- easy to back truck in without worrying about people walking thru lot.
Enter school through east door, looking toward gym/cafeteria to see what the situation is in there- make eye contact with anyone nearby.
Escort child to room, look at exhibit, acknowledge teacher, take picture. Tour a few rooms with child, after all, he will be going around with his class later. Stand in front of his class, remember that he left his lunch in the car (and make sure whatever he has "left" is not in his backpack.) Tell him to meet you at the east entrance in 5 minutes (there are clocks in all the halls). Leave him at the west end of the hall near his classroom. Go down the east stairs, exit through one of the cafeteria doors. Anyone there will notice you leaving alone.
Get in truck, keeping eye out for others in parking lot. Anyone who sees you will see you entering the truck alone.
Meanwhile your child has gone down the west stairs (maybe) and passed near the Main Entrance, where the office is. People in the office will have noticed him- may have noticed him, because the halls are not very full- the majority of kids haven't arrived yet. At that point, he's only a short walk from the east door.
Your car is in gear, ready to move. You see the east door start to open, and drive forward, stop under the portico and open the door for your passenger. Idle there half a minute, making sure he is not followed by a worried staff member. You have tinted windows, so no one can see who is in the truck. When you are satisfied that he has not been followed, drive away.
Point of vulnerability: he has five minutes to tell someone he's headed to meet you. Not likely, it's not interesting. At any rate, by the time someone is going to ask "Did you see him; what did he say", it's late in the day. The formal questioning was at the school 48 hours later. Any child who says, I saw Kyron, he had on his CSI shirt, and he was going to meet his lunch-provider, will/may be thought to be speaking of the previous day.
Point of vulnerability: Someone outside will see him getting into the truck. If they do, you will know it, because you will see them. Give him his lunch, he gets out of the truck and goes back to class.
Point of vulnerability: Someone inside will see him getting into the truck. Low probability from the gym/cafeteria. High windows, unlikely anyone is looking out and in the direction of the east door. The portico will make it even more difficult to see what is happening. And you've just gone through there, you know what people are doing and whether they're looking.
Point of vulnerability: Someone will be looking out the door and see him exiting. A staff member/teacher will have seen and stopped or followed him. A child might see him, but unless he says, hey, where you going, the event will go unremarked. And, thanks to the duplicate shirt, the previous day's east door pickup, and- the widely-disparaged comments from the boy and his granma -will all make it harder for a child's statement to be examined and believed. The kids probably weren't talked to for at least 12-48 hours later.
Chances of being seen are minimized. If a child says, I saw Kyron leaving with his parent, teacher thinks, Friday appointment. Or when the child is questioned later, the questioners will know that Kyron. wearing CSI shirt, left by the east door, into the truck on Thursday, because whoever picked him up will have said so, and the teacher has the record to prove it. Someone may have seen you going to or getting into your car-- alone. This is a good thing. Teacher will be anxious to claim that she thought the appt was this Friday, not next week. This is a good thing. School admin, although grieved about the disappearance, will minimize and deny their own negligence. This is a good thing, because their witnesses will say I saw the parent getting into her truck, and he/she was alone. I saw him/her drive away.
By the time anyone has to think hard and answer questions about what they've seen, it will be much harder to decide what happened on Friday.
That's all I've got, but here is the security info from the Handbook:
Building Security
All parents, visitors and volunteers are required to checkin at the office prior to entering any other portion of the building. Identification tags are to be worn by all adults in the building during school hours. For security purposes, only the main entrance and East door will be unlocked during school hours. All other doors will be locked or monitored, as required by our districts security policy. Please assist us as you enter or exit the building and check to see that doors are closed securely. If you are in our building and notice individuals without an identification badge, please ask them to register in the office.
No child is allowed to walk across the parking lot unattended.
PS I think the handbook is no longer on their site.
