Getting on at this school? (8)
I believe the answer is:
Here is my best explanation:
I believe this is a double definition.
'getting on' is the first definition.
('board' can be a synonym of 'get on')
'this school?' is the second definition.
(boarding school is a kind of school)
'at' is the link.
(Other definitions for boarding that I've seen before include "public school arrangement", "Living at school", "Staying at school", "Sort of party", "getting on", "Embarkation", "Getting on (a train)" and "-- School; -- pass".)