I read through this article expecting to agree with the findings, but surprisingly my experience was the complete opposite. My mother is a teacher and my younger brother is not a very good student. I found that as he struggled more and more, there was much less focus on my schoolwork. My mother focused more on cracking down on him and let me go my own way. While I stayed on more or less the same path, he recently just dropped out of college.
Surprisingly he also scored very well when he was tested for IQ (possibly close to my own scores, I do not remember).