Ian confused students altogether (2,3)
I believe the answer is:
in all
'altogether' is the definition.
(I know that altogether can be written as in all)
'ian confused students' is the wordplay.
'confused' is an anagram indicator.
'students' becomes 'LL' (two abbreviations for learner).
'ian' with letters rearranged gives 'ina'.
'ina'+'ll'='IN ALL'
(Other definitions for in all that I've seen before include "without exception" , "Everything considered" , "Altogether" , "Taken together" , "totally" .)