One thought is that both of these tests have content that are open to interpretation and can be impacted by impulsive selection of not-best options.
Like Odd-Item Out has a set of pictures and you have to select which one doesn't fit. Maybe a kid realizes that four of the five have A as the second letter, completely ignoring that 4 are fruit and one isn't.
Or for What's Missing, an example I've seen has an airplane with a wing missing. The first thing I noticed was that it was in the sky and there wasn't a pilot.
With age you may develop a wider base to notice more idiosyncracies making the selection trickier.
