As of its final Estyn inspection in February 2016, it had 824 pupils, down from 1,001 in 2009.

[1] Around one fifth of its pupils lived across the English border in Shropshire, and 18% spoke Welsh as a first language as of 2016.

The proportion of pupils with special educational needs was lower than the national average, and 6% qualified for free school meals, compared to a national average of 17.4%.

[1] As a bilingual school, Llanfyllin High School had a Welsh language stream in which most subjects were taught in Welsh, and an English language stream in which most subjects were taught in English.

[2][non-primary source needed] A group of pupils in years 6 to 9 participated in a project named Trochi (Immersion) to increase their fluency in Welsh and allow them to transfer to the Welsh language stream.