The Dallas ISD school was evacuated and classes were canceled earlier in the week because of high levels of carbon monoxide.
About 60 students and several staff members started feeling sick.
Part of the cause was a dead owl clogging up the exhaust system. The heating system also had a leak and the school district said that has been repaired.
Carbon monoxide levels were checked Friday afternoon, and they showed no leak.
The principal went around the school Friday, asking if anyone wasn't feeling well. Several children raised their hands.
In all,30 kids were checked out by the district's leading health official. Their blood pressure and temperatures were checked, and they were told to get some fresh air. After doing so, the majority of them said they felt better and were sent back to class.
However, eight of the kids who were checked out went home for things related to a number of symptoms, not just carbon monoxide, according to the district.
While carbon monoxide wasn't detected Friday, Lakewood parents say emotions are all over the charts.
"I think it's pretty mixed," said mom Julie Griffith. "I think everyone wants to feel comfortable about where they're sending their kids to school, and I think they're doing a good job of getting us there. I think some still need some convincing."
Seventy carbon monoxide detectors were also delivered to the school Friday, and sensors were installed in places like the basement.