Ruction occasionally in test for lesson (8)
I believe the answer is:
tutorial
'lesson' is the definition.
(I've seen this before)
'ruction occasionally in test' is the wordplay.
'occasionally' means one should take alternating letters.
'in' is an insertion indicator.
'test' becomes 'trial' (synonyms).
The alternating letters of 'ruction' are 'uto'.
'uto' inserted into 'trial' is 'TUTORIAL'.
'for' acts as a link.
(Other definitions for tutorial that I've seen before include "Teaching session for a small number of students" , "A period of individual tuition" , "Conference" , "Personal teaching session" , "Session of intensive teaching to an individual or small group" .)