The occupiers were dramatizing their frustration with plans by the Chicago Public Schools to close the school and reopen it as a charter.
Mayor Rahm Emanuel was forced to back off his unilateral closure of neighborhood branch libraries on Mondays after the move sparked a public uproar.
The mayor's plan will affect 10,000 students, mostly Black and Latino, and result in the firing of 600 teachers, principals, building maintenance, cafeteria and other workers.
They came to celebrate election victories in Ohio and across the country, the surging recall campaign in Wisconsin and the spreading Occupy movement.
Until recently, Chicago's Loop, known for its skyscrapers, corporate headquarters and high-powered law firms, was typically silent on weekends.
When Janet Edburg was laid off from her job at a Chicago photo lab equipment manufacturer three years ago, she experienced first hand the despair felt by millions of unemployed workers.
Several aldermen announced they plan to introduce an ordinance to decriminalize small amounts of marijuana caught on people by the police.
With the crowd chanting and drums and brass playing, the police slowly started surrounding the crowd.
Protesting the mass arrests and the destruction of their first aid station this weekend, ordered by Mayor Emmanuel, nurses and their allies picketed City Hall this morning.
During this week of action for jobs there are activities big and small all over Chicago.