Earlier this week, the Manhattan School District 114 sent a letter to parents, saying a school employee engaged in activity that did not align with school board policy.
The school district did not detail the allegations.
On Friday police said no criminal charges will be pursued.
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School officials said they were made aware of the allegations earlier this month. Manhattan police confirmed the teacher works at the junior high.
The teacher was placed on paid leave, it is unknown if they will be reinstated.
"The safety and well-being of our children are always paramount in our District, and we will continue to remain vigilant to proactively address any concerns that are brought to our attention," the district previously said.