School autonomy
But the head of Ark Academy in Wembley, Delia Smith, said: "We use setting at our school as the best approach for both teachers and students.
"Setting by subject is the best use of resources to focus teaching on individual children's attainment and ensure they are getting the appropriate challenge.
"When you have a student who may be struggling, setting can enable you to provide additional resources like teaching assistants or bespoke tools to support them to achieve their potential.
Head teachers' leader Brian Lightman said "professional decisions like this should be left to teachers".
"If schools are already achieving high standards within a mixed ability context, it is surely wrong to make them change because of a political whim.