Aitape BSP branch team members began working on the project in February and it was officially handed over on December 21 last year.
Aitape branch manager Alex Wafimbi said the project was a key part of team building exercise and to promote the organisation's values of, community, teamwork, leadership and people.
The project included the clearing of the project site, transporting building materials, the actual construction of the double classroom and loading gravel from the river to the construction site.
Lumi Primary School chairman Greg Ouke said: "This will really boost the morale of both the students and teachers and accommodate for effective learning to take place."