Thanks to students being lanky (4)
I believe the answer is:
tall
'lanky' is the definition.
('tall' can be similar in meaning to 'lanky')
'thanks to students' is the wordplay.
'thanks' becomes 'ta' (UK informal version of 'thank you').
'to students' becomes 'll' (**).
'ta'+'ll'='TALL'
'being' is the link.
(Other definitions for tall that I've seen before include "Unbelievable" , "Lofty; unlikely" , "that's hard to swallow" , "High in stature" , "Bigger than average" .)