Speakers included Merivale School principal and NZEI's Jan Tinetti and Aquinas College teacher and PPTA representative Graeme Bridge.
Ms Tinetti said the meeting brought together members from NZEI, PPTA plus groups covering support staff, early childhood educators, cleaning and caretakers.
''This is the first time in history this has happened, so you can see how important it is to our members,'' Ms Tinetti said.
Extra seating was opened up for the crowd, which overwhelmed original seating plans.
Today's meeting was one of 54 held around New Zealand, with organisers moving to Rotorua this afternoon.
Ms Tinetti said there had been massive support at all the meetings she had attended so far.
Ms Tinetti said if the proposed changes went through, it would have the single biggest negative impact on public education.
''It's important that we get the message to our members, then out to the community.
"It's huge, absolutely huge. That's why we are getting the turn-outs like this. People are really, really concerned. They want to hear the facts and what can be done.
''We are protecting the interests of the children. We are professionals. We have a very good understanding of what will be good for our children, This is not about us. It's about what we can put in place to ensure our children have quality education.''
A vote will be held after the speakers to decide what the unions will do.