hollye - I find your theory wholly plausible. The different staircases taken by TH and Kyron, IMO, are part of how Kyron was first seen in his classroom, etc, but more importantly, how TH met back up with Kyron to leave the school with him.
There is an element of human nature that, IMO, plays a part in how the different sightings of Kyron at school that day were recalled and reported. Typically, we are more acutely aware of ourselves, and what we are involved in than we are of others. So, since the science fair was a pretty important day, and the students had all put countless hours working on their projects, the bulk of concentration and energy that day would have been centered on just that. The times that Kyron was seen, or even the very last time anyone saw him within the school, or even in the classroom, could very easily have gone unnoticed in the buzz of activity. The students, teachers and staff who did report seeing Kyron may not be able to tell LE with accuracy exactly what time it was and where they where when they saw Kyron, not only because of the activity level in the school, but also because the normal routine was not being followed that day. With all of the above being said, I have to say that I am very dismayed that this case seems to have some of the elements of the Caylee Anthony and Hayleigh Cummings cases - the untruths, the untold stories that keep coming out, etc. Such a challenge for LE - certainly LE has not shared everything they know with the public. Praying for a break in this case soon - Kyron needs to be found - wherever he is.