MIDDLETON, Wis. -- School district officials said on Friday that Kromrey Middle School in Middleton will stay closed longer than expected -- through Sept. 10 -- as cleanup efforts continue after mold was found inside the building.

SLIDESHOW: Images From Inside Of Kromrey Middle School

Officials said that the school will be reopened after air quality tests are found to be within a safe and acceptable range, according to a district news release issued Friday afternoon.

Students had been scheduled to start classes for the year on Wednesday, but officials delayed the start of school as workers tried to clean up the mold. Officials said a white, difficult-to-see mold was seen in the building last week.

Middleton-Cross Plains Area School District Superintendent Don Johnson said that concerns about the mold's potential harmful effects prompted them to close the school. He said the mold isn't toxic, but is an allergen and can cause problems for students or staff with respiratory issues.

Johnson said that the building's floors, walls, ceiling and furniture will be cleaned. The superintendent had said that their original goal was to reopen school next Tuesday.

However, officials announced they were postponing the start date back further after determining the cleaning process "was more involved than originally judged by consultants."

In the news release, officials said that the Aspergillus/Penicillium mold that was found in the school was surface growth "due to the high humidity level in the school."

Officials said that some of the building's contents -- furniture, books, files and all cafeteria tables -- have been removed and discarded. They said that some items were cleaned, but some more porous items couldn't be safely cleaned. They said that a professional mold remediation company was cleaning the school.

It isn't known how students will make up the six days of school as yet, WISC-TV reported.

Stay tuned to WISC-TV and Channel 3000 for continuing coverage.