Show disapproval with introduction to alternative teacher (5)
I believe the answer is:
tutor
'teacher' is the definition.
(I know that tutor is a type of teacher)
'show disapproval with introduction to alternative' is the wordplay.
'show disapproval with' becomes 'tu' (I can't justify this - if you can you should give a lot more credence to this answer).
'introduction' indicates taking the first letters.
'alternative' becomes 'or'.
The initial letter of 'to' is 't'.
'tu'+'t'+'or'='TUTOR'
Can you help me to learn more?
(Other definitions for tutor that I've seen before include "Master" , "Personal coach" , "college teacher" , "trainer" , "He shows us the way" .)