Now that it covers pre-Academy Coal Hill, this page probably shouldn't be directly at Room A19, as it's unlikely and, most importantly, not confirmed that it was at the same room number in the 1960s.
Might I suggest Head's Office, the actual term used in Time and Relative, to be neutral to the change between "headmaster" and "headteacher"?
Talk about it here.
The Head's Office (PROSE: Time and Relative) was the head teacher's office at Coal Hill School, and so belonged to the incumbent head teacher. Following the renovation of Coal Hill, it was located in Room A19 of the Barbara Wright Building. (TV: Co-Owner of a Lonely Heart)
Coal Hill School
Mr Okehurst sent Susan Foreman and Gillian Roberts to the Head's Office after he suspected them for what an animated snowman did to Francis Minto. The headmaster, Mr Carker, gave them both detention, and sealed notes to give to their parents. (PROSE: Time and Relative)
Coal Hill Academy
Frank Armitage's office had red walls, upon which hung portraits of various gentlemen. Two bookcases, full of old books stood behind either side of his desk, one of which had trophies on the top shelf. A clock was on the wall opposite the desk. The office also contained a filing cabinet, a chess set and a hand-held school bell. (TV: The Coach with the Dragon Tattoo)
Miss Quill met with Mr Armitage in his office after verbally abusing Paul Smith. He told her not to get into any "special measures" as "the Governors wouldn't like it". (TV: The Coach with the Dragon Tattoo)
April MacLean, Charlie Smith and Tanya Adeola went to see Mr Armitage in his office to ask about the disappearance of a cleaner. During their visit, Mr Armitage was skinned alive and subsequently killed by a skin-peeling dragon while trying to protect them. (TV: The Coach with the Dragon Tattoo)
Dorothea Ames' office had green walls and seemed more spacious than that of Mr Armitage. In the centre of the wall behind her desk was a modern-style bookcase, with frames of preserved butterflies hanging at either side. Ames kept files in her office, for the attention of the Governors and pertaining to certain individuals including Charlie Smith, Andrea Quill and the Doctor. The office contained a bowl full of multiplying killer petals, which Ames monitored and learnt from. (TV: Co-Owner of a Lonely Heart)
When Miss Quill visited her office, Dorothea questioned the aliases "Charlie Smith" and "Andrea Quill". She suggested that she worked with the Governors and asked Quill to help them with the invasion of killer petals. In return, she offered to remove the arn and give Miss Quill her free will back. (TV: Co-Owner of a Lonely Heart)