Mixed ability is the normal condition

Not a problem to be solved once, a permanent design constraint.

Every class is mixed, because a level band covers a range and because skill profiles differ within a band. Teachers are frequently advised to differentiate, which in this setting usually means preparing multiple worksheets, and that is unsustainable across a full timetable.

What is sustainable is task design with a low entry and a high ceiling. A speaking task everybody can attempt, where stronger students naturally produce more complex language, occupies the room without requiring parallel materials. So does a text everybody reads with questions of graded difficulty.

Pairing is the other tool and it needs deliberate use. Stronger with weaker helps the weaker and can bore the stronger; matching by level produces better practice at the cost of exposure. Alternating deliberately, rather than letting students self-select, distributes both.

The students most often lost in a mixed room are the quiet middle: not struggling enough to attract attention, not strong enough to lead. Tracking who has actually spoken in a lesson, crudely, reveals how uneven participation usually is.

The other reason to review placement in the first week is that test performance is affected by circumstances. A student who sat the placement test the day after a long flight, or in the middle of a crisis at home, has been measured at their worst, and nothing in the process corrects for it unless somebody looks again.