For those of us with mathemetically precocious children, we can sometimes be stumped when they have an unexpected blind spot where they don't seem to understand or realize something that we think should be "obvious".
lol, yea this. Tuesday, DS7 invites me to sit with him as he tries out (another) math site. He's taking a test on middle school statistics. The last question is what is the mode of the data, he looks at me like "what in the world are they talking about?" I knew over a month ago he was talking this from a podcast. So, just short of sighing, I ask him "You know what mean is?" Yes. "And median?" Yes. He chuckles and says "oh yeah, mode is the most one."
Honestly, I doubt if 5% of people on the street know the difference between the three but somehow I expect a seven year old to? Or perhaps more similar to your thought, lowest common denominator has been a particular gap of his.
