I am not a Halachic authority, but I believe that since the door is closed
but not locked ie, the school secretary, teacher, psychologist, principal,
etc. can walk in, and there are open windows it is permissible. This is
based on a P'sak (halachic ruling) which my batchelor friend received from
the Late Bostoner Rebbe R' Moshe Horowitz of blessed memory that since his
car had windows, it was permissible to be with a female date even at night
and it would not constitute Yichud - based on the fact that he would be on
public roads or streets and not parked in an Orchard or some lonely dirt road.
Be well,
Richard (Rachamim) Pauli