Call the old students (4)
I believe the answer is:
yell
'call' is the definition.
(I know that call can be written as yell)
'the old students' is the wordplay.
'the old' becomes 'ye' (resembles a historical spelling of 'the').
'students' becomes 'LL' (two abbreviations for learner).
'ye'+'ll'='YELL'
(Other definitions for yell that I've seen before include "Shout - Shetland island" , "Clement --, politician" , "Shetland isle" , "Shout loudly" , "Call out" .)