It’s the % of aim records (starts or leavers depending on how you like your terminology!) that fall below the minimum standard (MS) set for the aim type.
It is done at aim level, by applying the aim type, then seeing how big the cohort below MS is, as a proportion to all records. If above 40% then it may trigger intervention.
As a basic example:
100 aim records on an English functional skill with overall achievement at 61% (were MS is 63%. all these count as below MS)
100 aim records on a Maths functional skills with overall achievement at 65% (MS is 63%). All these count as above MS.
So 100/200 = 50% of the provision would be below minimum standard.
(don’t confuse it with the fact that a combined 128 of the 200 achieved (64% overall achievement))
Bit of a crude method for ‘buying’ quality provision in my opinion – L1 & 2 national averages in English and Maths are comfortably below 63% – so you could be significantly out performing the average and still be under threshold if you have no other substantial provision to balance it out (I know of providers who have pulled provision that is above the national average, but below MS, displacing learners to providers with lower rates…)