Conversation so far:
Where was Pierre Monteux first a conductor?
At the age of twelve, Pierre Monteux organised and conducted a small orchestra of Conservatoire students to accompany Cortot in performances of concertos in and around Paris.
Where was Pierre Monteux a conductor for the first time?
At the age of twelve, Pierre Monteux organised and conducted a small orchestra of Conservatoire students to accompany Cortot in performances of concertos in and around Paris.
Does your article ever show Pierre Monteux as a conductor?
Yes, there are several photos of Pierre Benjamin Monteux was a French (later American) conductor.

Question: What performance was that?
Self-contained rewrite: What performance was displayed on the article with Pierre Monteux conducting?