Conversation so far:
Where did Massiaen grow up?
Olivier-Eugene-Prosper-Charles Messiaen was born December 10, 1908 in Avignon, France, into a literary family.
Who were his parents?
He was the elder of two sons of Cecile Sauvage, a poet, and Pierre Messiaen, a teacher of English who translated the plays of William Shakespeare into French.
How many siblings did he have?
CANNOTANSWER.
Where did he attend school?
At the Conservatoire, Messiaen made excellent academic progress.
In 1924, aged 15, he was awarded second prize in harmony.
What did he study?
After showing improvisational skills on the piano Messiaen studied organ with Marcel Dupre.

Question: Who else did he study with?
Self-contained rewrite: Besides Marcel Dupre, who else did Olivier Messiaen study with?