I really don't understand how this statement is even remotely true.

The only thing I can think of is that "coaching" is too broad--ie. includes both students who spend 100+ hours and students who spent an hour at a talk by the guidance counselor.

Doing nothing other than taking a couple sample tests has to net you a bunch of points because you don't have to waste time reading the directions.

Simply drilling basic mathematics so I could do "1+1" and come up with 2 regularly netted me almost 250 points in Math (standardized tests like the SAT are really nasty about having answers that match the common mistakes).

Going through 6000 vocabulary words pulled my verbal up almost 250 points (and had a dramatic effect on my writing). But that's far beyond "coaching" ... that's a multi-year commitment.