Heavyweight head dismissed from school in Berkshire (3)
I believe the answer is:
ton
'heavyweight' is the definition.
(a ton weighs a lot)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for ton that I've seen before include "People of fashion" , "Speed" , "20cwt" , "Unit of weight equivalent to 2240 pounds" , "Fashionable" .)