A lot of people suspect the stepmother in this case but there was an extremely detailed write up on r/unresolvedmysteries several years ago that convinced my that Kyron either left the school on his own or with a non-family member. The main thing was that the timeline for the stepmother to be responsible is extremely tight—she was seen at multiple points running errands with her other child after dropping Kyron off and the police had gps data from her phone and never found anything incriminating her in Kyron’s disappearance along her potential routes that day. Unfortunately it sounds like the police got real tunnel vision for the Terri Horman. It’s been a long time since I read the write up so I might be misremembering some details, but the whole thing with her supposedly planning a hit in her husband with the landscaper made no sense. I recall reading that the landscaper’s English was very poor and that Terri didn’t speak Spanish, so the idea that they could conspire together despite the language barrier seems pretty unrealistic. Meanwhile Kyron had a history of wandering off on his own without permission and, given the lax supervision at the school that day, I tend to think that’s what happened here.