Parents in the school community were told at a meeting last night the school would literally be picked up and moved across the road, from its present site in Church St, at the end of this year.
Diocese general manager Stuart Young said the school was prefabricated and could be easily moved in pieces to the new site next to the Holy Cross Conference Centre.
The relocation would begin at the end of term 3 with the removal of two classrooms from the present site. The remainder would be shifted at the end of the school year.
Despite using existing school buildings for the new school, Mr Young said pupils might not recognise them when the work was completed, because they would be rearranged from long banks of classrooms to a "pod-shape" on the new site.
"It's not a cheap exercise. We have to form new roadways, build a new playground and do a bit of landscaping.
"The buildings will also be modernised in the process. It will cost about $2 million," he said.
It was planned to have the new facility open in time for the start of the 2013 school year.
Mr Young said the move would provide the school with a larger play area, it would connect to neighbouring sports fields and the site would "future-proof" the school for expansion as Mosgiel continued to grow.
While the design of the new school was not a secret, the identity of the new owners of the site being vacated by St Mary's School was.
"The land has been sold. But I'm not at liberty to say who it was sold to."
