Parents in a Middlesex County town are frustrated and concerned with school officials after they say that their children were exposed to unhealthy levels of carbon dioxide.

Middlesex Borough school officials say that they are working to fix the problem at Von E. Mauger Middle School. A county hazmat team was at the school Tuesday.

But parents say that the school knew about the issue for a while and did not tell parents.

"This is not acceptable. You're subjecting our teachers and our children to unhealthy air,” says parent Lisa Giacone.

Dozens of parents attended a school board meeting Monday night and demanded answers from school administrators. They wanted to know why the levels of carbon dioxide were so high and they wanted to know what was being done to fix the problem.

Samuel Kleiber stayed home from school Tuesday. He says that he and other classmates are finding it hard to concentrate due to the exposure.

“About a week ago I started getting drowsy. I was falling asleep while I was in class,” the seventh-grader says.

District officials say they first found out about the issue in the spring, but that it wasn’t until a second employee complaint was filed in September that they took a bigger look at the problem.

Health Department officials visited the school on Sept. 14 and took readings in 18 classrooms. Nine classrooms were above the acceptable level of 1,000 parts per million, according to the report.

“[The Health Department] indicated to us that there was no reason to close the school, that everything was safe to be occupied but we should remediate these things as soon as possible,” says Superintendent Dr. Linda Madison.

Dr. Madison says that the school is now replacing parts in the ventilators to fix the problem.

But parents say that they want a quicker solution, and say that the school should be closed until the problem is fixed.

“This is now. The kids are going through this now and nobody should be in that school in that condition,” says Ann Maria Kleiber.

The superintendent tells News 12 New Jersey that she did not know that any children were sick until Monday night’s meeting. She says that she has asked the school nurse for a report to look deeper into the issue.