"All the hospital reports are saying those 10 minutes were critical and we got on to it straight away, and that made the difference to her," Mr Coleman said.
Other staff also helped at the scene before paramedics arrived and Mr Coleman said support was being offered to both pupils and staff.
Seniors were away on exam leave, but juniors, years 7-10, were still in class.
Mr Coleman said pupils' routines had not been disrupted and that was probably helping them through the situation.
Meanwhile, senior staff were monitoring teachers remaining in class to ensure they were okay.
"I think we've done a huge amount to support the staff and everyone's looking after each other, which is fantastic."
The community had also rallied around, with some people dropping in food.
"We've been thinking a lot about Jo and hopefully she's going to pull through."
Mrs Nicolson is in Timaru Hospital and a spokeswoman there would not give a condition update, saying the family had requested privacy.
But this afternoon the school posted an update on its Facebook page, saying: "We have heard this afternoon that Mrs Nicolson is continuing to breath on her own and that the fantastic Timaru Hospital staff are continuing to work hard on her recovery. No more updates as yet.
"Thank you to everyone who has sent their thoughts, prayers and best wishes to us for Mrs Nicolson and her family."
An earlier update said Mrs Nicolson had suffered a cardiac arrest and was in intensive care.
Mrs Nicolson, aged in her 60s, has been at the school for about a decade.
