@ Patrick, because le + an = leis an...
Not to be confused with le + é = leis (liom, leat, leí, etc for mé, tú, í, etc)
@Mary, I felt you way is more natural, but sentence creator may have chosen to be literal.
Why not sheinn muid?
Both are equally valid.
Report it with the little report flag if it is not accepted (putting it in this discussion is not likely to make a difference).
Sheinnimid is not ok?
The -imid ending is the present tense ending for the first person plural.
Why leis and not le in this sentence?
I thought that a'location descriptor' should come at the end of this sentence.
The order of adverbial phrases in an Irish sentence is place, then mode, then time, so san ollscoil is properly placed before leis an léachtóir above.
Since ceol is an abstract noun being used in a general sense in this sentence, an ceol should also be accepted for “music”. (It’s been reported.)
The specific music that was played isn't abstract.
You might have a case if the verb was rinneamar staidéar ar, but not with sheinneamar.