The original article already provided evidence, based on analysis of the performance of similar students who do and do not get into a selective school. As it says...
"Except that attending those high schools simply doesn’t matter in terms of conventional educational outcomes. When you look at the edge cases – when you restrict your analysis to those students who are among the last let into such schools and those who are among the last left out – you find no statistically meaningful differences between them."
So unless you're calling out the original article, how about offering counter-evidence?
Eh, not really. I've learned over the years to avoid providing sources because more often than not the person won't believe you either way and will only use the source as a tangible target for disingenuous attack through motivated misinterpretation. (https://en.wikipedia.org/wiki/Motivated_reasoning)
I typically provide sources in response to replies like: "That's interesting, but I can't really find anything on the matter; can you point me to something?" But if there is no indication that the person actually tried to find corroboration independently I take it as a sign that he is not actually interested in corroboration. I'm sure this is inaccurate sometimes, but it's the best approximation I can come up with.
"Except that attending those high schools simply doesn’t matter in terms of conventional educational outcomes. When you look at the edge cases – when you restrict your analysis to those students who are among the last let into such schools and those who are among the last left out – you find no statistically meaningful differences between them."
So unless you're calling out the original article, how about offering counter-evidence?