The linked article fails to make an important separation of two factors. Hopefully the actual research paper addresses this.
In a gifted/tracked class two things may happen.
(1) The peers are stronger.
(2) More advanced material is taught.
It is unsurprising if (1) has little or no effect. But surely (2) teaching more advanced material, should lead to more advanced learning, and higher test scores. I can think of various reasons why this may not be found in certain situations, but it is abysmal journalism that the difference between (1) and (2) was not addressed.
