There was extra security at Hop Brook Elementary School in Naugatuck on Tuesday morning after two knives were found in the school over the span of a week.
On Monday, police were called to the school as a precaution after a fourth-grade student found a kitchen knife in the bathroom.
The Board of Education is also investigating.
This is the second time in two weeks that a knife has turned up at school.
Last week, a third-grade student found a folding knife in her locker and reported it to the school, police said.
School officials are trying to find out how both knives wound up in the school and periodic sweeps of the school are planned.
"Somehow they're ending up in school and don't belong there," Supt. James Connelly said of the knives. "We take it seriously."
Connelly said security is in place at the front of the school before and after the school day and that a guard will sweep the locker area "for the forseeable future."