Yes, I think that's probably true-- and moreover I think that even if
g didn't drop, intelligence scores could well drop. When I did some light reading in this area last year, I recall that training is believed by many, based on adoption studies etc., to have a fairly large positive effect (2/3 - 1 SD IIRC) on IQ in the short term, and less (1/3 SD or so) long term. It makes sense to me that depression and lack of stimulation could have a large negative temporary effect as well. However, I also think that an assumption that the highest score is the most accurate sounds like the wishful thinking of an overly competitive parent.
http://en.wikipedia.org/wiki/Heritability_of_IQ"Dickens and Flynn (2001) argued that the "heritability" figure includes both a direct effect of the genotype on IQ and also indirect effects where the genotype changes the environment, in turn affecting IQ. That is, those with a higher IQ tend to seek out stimulating environments that further increase IQ. The direct effect can initially have been very small but feedback loops can create large differences in IQ. In their model an environmental stimulus can have a very large effect on IQ, even in adults, but this effect also decays over time unless the stimulus continues (the model could be adapted to include possible factors, like nutrition in early childhood, that may cause permanent effects). The Flynn effect can be explained by a generally more stimulating environment for all people. The authors suggest that programs aiming to increase IQ would be most likely to produce long-term IQ gains if they taught children how to replicate outside the program the kinds of cognitively demanding experiences that produce IQ gains while they are in the program and motivate them to persist in that replication long after they have left the program."
http://www.brookings.edu/views/papers/dickens/20020205.pdf
