CHICAGO -- City inspectors gave a Chicago elementary school a failing grade this week on their clean-up efforts for rodent infestation.

CBS Chicago reports Monday's walk-through at Mollison Elementary School found 285 mice droppings scattered throughout Pre-K classrooms, the library and the staff lounge. Inspectors labeled it a critical health violation.

The walk-through comes after Chicago Public School (CPS) officials said they exterminated and performed a "deep cleaning" over Thanksgiving break.

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"We like open up some of the storage closets, let's look in places where people don't expect you to look – behind stuff, in corners – and it was still a lot of mice droppings," said local school council chair Yolanda Redman.

A photo posted to the Chicago Teachers Union (CTU) blog is said to show just one of the critters wreaking havoc on the school.

"It's been ridiculous," said local school council vice chair Danielle Lester. "It's been kids running from them, trampling over one another and things like that to get rid of them and everything."

The CTU blames CPS' janitorial services, which were recently privatized.

A CTU statement released Wednesday night reads in part: "Problems with the companies, from filthy classrooms to vermin infestations, began to surface immediately."

On Monday, parents sent CBS Chicago a video of children apparently helping with the latest round of rodent cleanup. CPS representatives said it is unacceptable, and that they have spoken with school administrators about the children's involvement.

CPS said they installed 300 rodent traps last week and after Monday's failed inspection promised a pest control expert on-site daily.

Students have not been able to buy hot lunches since the beginning of the week.