Landsdale Gardens Adventist School principal Mark Foster said works on a high school building began in April and would be completed by the 2016 school year.
He said the $2 million two-storey facility being built by TM Construction included classrooms, general learning areas and space for art, science and food.
"We're up to pouring the suspended slab at the moment; we�ve got the roof going on in the next week or so and windows in the next month," Mr Foster said.
Get in front of tomorrow's news for FREE
Journalism for the curious Australian across politics, business, culture and opinion.
READ NOW"At the moment it's choosing internal colours and flooring so the interior design."
He said the second stage of the plan included the construction of a $2 million early learning childhood centre.
"So a K-2 building and we're looking at getting that right out the front of our property just to get the exposure " we�ve got a 40,000sq m footprint and we're only taking up a small percentage at the moment,� he said.
"We're just going to build out towards the road so people don't drive past and wonder where we are."
The Queensway Road school, which has operated as a primary school for more than 20 years, was given Government approval for high school enrolments two years ago and currently caters for students up to Year 10.
"From 2013 was our first high school year and then 2014 we had Year 9s and then our Year 10s in 2015 and then next year we�ll have Year 11s, so by 2017 we�ll be a K-12 campus," Mr Foster said.
�We're basically getting the infrastructure in place so this building will handle the growth that we currently have and expand our high school program.
"Our next building will be in about two years time, so every two years we're looking at adding on some new infrastructure to sustain the growth."
He said the school was also expanding the play space for the kindergarten and pre-primary students and the Year 5 and 6 students were creating a garden.
"Where we are situated is a growth area and we have a few other Adventist schools in WA " there's only one other high school, which is in the Hills " so we were really keen to establish another Christian school in the northern suburbs," he said.
"For however many years we were just K-6 but now we�ve got the opportunity to expand to high school and cater for a different need."
The school will hold a car boot sale on Sunday, September 13.