I don't agree with that at all. Endless piles of money have been thrown at trying to "fix" the achievement gap between racial groups. It has persisted unchanged for the last 50 years. There are genetic, cultural, political and societal reasons behind the problem. If you cherry pick some individuals on the high end of the IQ curve and shelter them from the negative cultural influences, you might succeed. In the real world where the socialists force a room of mixed ability children together and teach to the the capability of the least capable child in the room, you get crappy results. Separate them by ability and teach of room full of similarly capable students. You'll get a better result. Intelligence is not improved by osmosis.
I do agree that you can create a room full of children that can all fail together. It is done daily in the public schools.
Many schools still have teacher IAs pull low-achieving students out of class and have them work in small groups.
Unfortunately many districts across the country are laying off teachers and IAs so more money can go to useless programs which amount to nothing but restrictions on the curriculum. I hear teachers complain about this all the time. The people who actually care about the kids are not allowed to do their jobs.