Write lines about school being poor (9)
I believe the answer is:
penniless
'poor' is the definition.
(similar in meaning)
'write lines about school' is the wordplay.
'write' becomes 'pen' (synonyms).
'about' indicates anagramming the letters.
'school' becomes 'S'.
'lines' is an anagram of 'niles'.
'pen'+'niles'+'s'='PENNILESS'
'being' acts as a link.
(Other definitions for penniless that I've seen before include "Jack in New York" , "Broke" , "Skint, without a cent" , "Not rich" , "Very poor" .)