Teachers at Patton Elementary in Riverdale on strike

CHICAGO (CBS)-- Grade school teachers in South suburban Riverdale are on strike.

Teachers at Patton Elementary have been in negotiations with District 133 for nine months.

The district is offering a 16.5 % pay raise over four years, but the union wants an 18% increase over three years.

The union also wants to remove "antiquated and unnecessary" language about teacher dress code.

The school is open Tuesday for parents who need to drop off children.