I like to move the discussion to a different genetic variant that people are generally more comfortable discussing...height. Your kid has a genetic code that will allow him to be very tall (over 7ft). If he eats properly and avoids disease, injury, or growth-stunting medication, he will max out that potential. You could take in another student that could be 6'10 or 6'8 or maybe only 5'7 with those same conditions. Maybe you give that kid some hgh and they end up taller than yours. It is obviously not a perfect analogy for nature vs nurture, nor does it take into account some of the short-comings of using iq score as a proxy for intelligence, but it works for me.
