Mr Caldwell said it had been "a horrible time" when part of the school had burned down, but in the aftermath teachers had acted with the utmost professionalism, even though they had lost everything from their classrooms.
"I was proud of them and of the students who had their classes at neighbouring St Patrick's School until temporary classrooms were made available on the school grounds. Students and teachers did the job to the best of their abilities."
The opening speeches were followed by a stirring haka led by student Bruce Macauley then the whole school sang Kiwi Kids Are Rockin' It.
Two pou or carvings on the front of the class block were unveiled - a small one representing junior students and a taller one to represent the seniors with the distance between signifying the growth in learning.
Mr Caldwell described the colourful classroom set up as a modern learning environment with six actual classrooms opening out to other flexible spaces.
Tables of different heights, ergonomic furniture, open spaces and quiet learning spaces would allow for different learning styles and activities.
The school also has a bilingual unit for Te Reo and English with a mix of Maori and pakeha students.
Some of the temporary classrooms would also remain on the grounds to accommodate the growth in the school roll since the fire.
"The current roll is 220 and by the end of the year the roll will have grown by 100 since the fire.
"Class sizes are generally around 25 children."
The new classrooms had been in use since the start of term one with the official opening delayed until everything had settled in.
Mr Caldwell said it was an opportunity to acknowledge the community.
"I've been really humbled by the support from Kapiti and other parts of New Zealand.
"The South Wairarapa District Council sent us many library books to replace the ones we lost.
"This school is 125 years old and we lost all our records, but people were coming in with photographs of their classes to help us rebuild our archives.
"We want to thank all those people who donated in whatever capacity.
"It's been a long three years in some respects but I'm thankful for where we are."
The Board of Trustees is inviting anyone interested to go along to the school for an Open Day on Sunday May 14 between 2pm and 4pm to see the new classrooms and facilities.