[cowsandmilk]

> The parent made no error in his language.

The parent claimed a 3-4 point in an individual's IQ is statistically meaningless by point to the standard deviation of IQs for an entire population. That is either (a) misguided or (b) intentionally misleading.

The standard deviation of a non-identical population has no relation to the statistical significance of a change for an individual.

Let's say the standard deviation of heights for males is 2.8 inches; that is what some of the internet claims. Let's use two standard deviations as statistically significant. That means, if someone woke up one day and was 6'3" instead of 5'10", that was not a "significant change" because they only changed in height by 5 inches.

Standard deviation for a non-identical population is completely unrelated to the significance of changes for an individual.