Keep the following numbers in mind for the next time a public-sector union official starts lecturing you about social justice.
In Chicago, 85 percent of the roughly 400,000 public school students are either African-American or Latino. A similar percentage receives free or reduced-price meals, which means these students live at or near the poverty line: $27,214 for a family of three, in a typical case.
The average public-school teacher in Chicago earned almost triple that amount - $76,000 per year, according to the school district. In contract negotiations this year, Chicago Public Schools offered an average total pay increase of 16 percent over four years.
The Chicago Teachers Union, 26,000 strong, rejected the offer and went on strike Monday, sowing chaos among children and parents.
No one can say how long this walkout will last, but even if it ends tomorrow it has already harmed poor minority children, upon whose education the future of Chicago, and the country, depends.
I cannot describe the moral repugnance of this strike by aggrieved middle-class "professionals" against the aspiring poor. Well, I could describe it, but only by plagiarizing Chicago Mayor Rahm Emanuel's unprintable vocabulary.
So let's just say events in Chicago illustrate rather dramatically the contradictions between public-sector unionism and the efficient delivery of vital public services.
They also heighten the contradiction between the Democratic Party's need to show it can deliver sustainable good government and its dependence on public-sector unions for political funding and get-out-the-vote foot soldiers.
Common sense says there should be some link between compensation and job performance. But the very idea tends to make teachers unions recoil like Dracula confronted with a garlic clove.
And so the Chicago Teachers Union is picketing schools that graduate only 60 percent of their students and where fewer than 8 percent of 11th-graders met all four college readiness benchmarks on 2011 state tests, according to the school system.
To his credit, Emanuel decided to shake things up when he took office last year, even if it meant tangling with the teachers union. He rescinded an unaffordable pay increase and called for a 90-minute extension of the school day, which, at six hours, was one of the shortest in the nation.
That infuriated the teachers union; a truce was reached when Emanuel agreed to rehire laid-off teachers to handle the extra workload.