What pupils learn about in maths class — talk about noise! (8)
I believe the answer is:
ordinate
'what pupils learn about in maths class' is the definition.
I can't tell whether this definition defines the answer.
'talk about noise' is the wordplay.
'talk' becomes 'orate' (to orate is to give a speech).
'about' means one lot of letters goes inside another.
'noise' becomes 'din' (din can mean a loud noise or disturbance).
'orate' enclosing 'din' is 'ORDINATE'.
Can you help me to learn more?
(Other definitions for ordinate that I've seen before include "It goes with abscissa in plotting a point" , "Distance of a point from the x-axis" , "Line of mathematics" , "Roman garment" , "Straight line parallel to an axis" .)