Conversation so far:
Where did Olivier Messiaen grow up?
Olivier Messiaen was born on December 10 in 1908 at Avignon, France.
Who were Olivier Messiaen's parents?
Olivier Messiaen is the son of Cécile Sauvage, a poet, and Pierre Messiaen, a teacher of English.
How many siblings did Olivier Messiaen have?
Olivier Messiaen was the elder of two sons.
Where did Olivier Messiaen attend school?
Where did Olivier Messiaen study?
Olivier Messiaen entered the Paris Conservatoire in 1919, aged 11 and studied music.

Question: Who else did he study with?
Self-contained rewrite: Who did Olivier Messiaen study with in his youth and early career?