Teachers and District 46 school board officials in Grayslake worked up until the Tuesday night deadline to avoid a strike but ultimately couldn't make it happen.
Roughly 4,000 students will not have class until a deal can be reached.
The teachers have been working without a contract since July, and salary remained the big sticking point in the final hours of talks. The district has posted on its website proposals made to teachers in October and November of last year.
District 46 teachers currently earn an average of $57,000 per year.
"We have a board that's largely been held hostage by three or four board members who are very, very anti-tax. Nobody's pro-tax but the fact of the matter is these are some of the lowest paid teachers in the surrounding district," Mike McGue, the Lake Count Federation of Teachers President, said late Tuesday.
"It put us in a burden to have to pay someone to watch our kids, or some of the parents are not going to be able to go to work," said parent Aaron Feldman.
Veteran fourth grade teacher Tracy Danielson described the situation as "scary" and "anxious."
"No one knows what to expect," she said.
The district includes eight schools: Grayslake Early Childhood Education Center, Avon Center School, Meadowiew School, Prairieview School, Woodview School, Frederick School, Grayslake Middle School and Park Campus.
Grayslake Patch has collected childcare information for parents in the event of a strike.