In fact, the study shows that mixed ability and setting both “hurt” students with lower prior attainment, because both models involve persistent low levels of progress for those students. Ability grouping “works” in that it favours the strongest performing, like much else in ed.
Ability grouping, with appropriately tailored curriculum, helps high-achieving students and does not hurt others.
The research has pointed this way for a century despite generations of propaganda to the contrary, but it's good to have another reminder. Ability grouping works.