École St. Joseph School in Yellowknife will receive three new modular classrooms and a washroom facility in a set of upgrades worth $1.5 million.
The territorial government is providing the portables in response to an internal report suggesting Yellowknife's student population will increase by 200 in the next nine years.
Yellowknife Catholic Schools will be able to accommodate an extra 66 students once work is completed, with the replacement of JH Sissons School – due in the net few years – expected to offset any additional demand.
The new facilities at St Joe's are scheduled to be ready before the start of the 2018-19 school year.
"Increasing enrolments across the city have necessitated a plan to increase structural capacity over the next five years, and the modular classrooms are the first step in addressing these needs," said education minister Caroline Cochrane in a statement.
The announcement comes while the territory defends its school funding formulae in the face of protests from parents of students at francophone schools in Yellowknife and Hay River.
École Allain St-Cyr and École Boréale both stand to lose teaching and support positions as a result of a drop in their student numbers and a territorial requirement that specific inclusive schooling positions be filled.
By contrast, the territory says St Joe's is at 98 percent capacity. Ordinarily, school space is reviewed when attendance reaches 85 percent of space available.