Waterford — Much of the exterior work on the new high school building is complete and work is under way inside the building’s classrooms, auditorium and meeting spaces.

The $67 million construction project, which began in December 2010, includes a 5,000-square-foot media center, a mezzanine-level skywalk that will connect a portion of the old Waterford High School to the new addition next door, and extensive technology upgrades.

The project calls for an approximately 125,000-square-foot, three-story addition, renovation of about 106,000 square feet in the existing high school and demolition of the remaining 125,000 square feet in the existing school.

Teachers and students are expecting to move into their new building in April 2013, two months later than planned.

They were supposed to move into the building in February, but Superintendent of Schools Jerome Belair said Tuesday that the excitement of the new building and how foreign it will be to students could create anxiety. He does not want the teachers or students to have to adjust to a new building and also be ready to take the Connecticut Academic Performance Test in March.

He said the extension will allow for another week and two additional weekends for the final touches to be added to the building.

“We’re on a very aggressive schedule,” Belair said. “We’re making nice progress.”

He added that the project is about $1 million under budget but that he does expect some additional, unplanned costs.

In March, construction was about $2.5 million under budget.