Teachers' publication holds clear beliefs (6)
I believe the answer is:
tenets
'beliefs' is the definition.
('tenet' can be a synonym of 'belief')
'teachers' publication holds clear' is the wordplay.
'teachers' publication' becomes 'tes' (Times Education Supplement).
'holds' means one lot of letters goes inside another.
'clear' becomes 'net' (as in net profit).
'tes' going around 'net' is 'TENETS'.
(Other definitions for tenets that I've seen before include "Conviction" , "We stand by these" , "Convictions" , "Principles, beliefs" , "Doctrines of belief" .)