I don't see what's wrong with a low sample size.

The usual things -- the results are at best brittle and worst just a figment of someone's imagination.

Almost all of the participants improved and by a statistically significant amount.

Yeah, well, that's a problem :-/

I eyeballed the IQ improvement graph for the intervention group and converted it into numbers. By the way, there are only 13 lines there, so either someone's results exactly matched some other person on both tests or they just forgot one.

The starting values are (91 96 99 102 105 109 109 113 122 133 139 139 145)

and the ending values are (122 113 109 118 133 99 118 123 151 133 145 151 151)

The deltas (change in IQ) are (31 17 10 16 28 -10 9 10 29 0 6 12 6)

So what do we see? One person got dumber by 10 points, one stayed exactly the same, and 11 got their scores up. Notably three people increased their scores by more than one standard deviation -- by 28, 29, and 31 points.

Y'know, I am not going to believe that a bit of association training between letters and colors will produce a greater than 1 sd increase in IQ for about a quarter (23%) of people.