Chicago public teachers walked out on 350,000 students today, the first strike in a quarter-century at the nation's third-largest school system.

It's hard to have much sympathy for the strikers: At an average of $76,000 per year before benefits, they are the highest-paid big-city teachers in the nation. (Paradoxically, Chicago's per-student education expense is relatively low.) Union leaders initially asked for an increase of nearly 30 percent over two years; Mayor Rahm Emanuel offered a 16 percent pay raise over four years, which doesn't seem too shabby amid a high unemployment and a sluggish economy. The union points out that Emanuel rescinded 4 percent raises over the summer and is lengthening of the school day and year (Chicago teachers now spend less time in the classroom than their counterparts in any other large city.)

Not all Chicago pupils will be enjoying this Indian-summer break, however. For the 52,000 who attend public charter schools, it will be business as usual -- and business is pretty good. Chicago has roughly 100 charters. Such schools are publicly funded but usually non-union and mostly autonomous in terms of curriculum and finances. Chicago plans to create 60 more within five years. The windy city ranks behind only New York City in the Brookings Institution's most recent Education Choice and Competition Index.

Academic success, as with most charter programs, has been mixed. A 2009 Rand Corporation study found that students who attended Chicago's "multi-grade" charters (including middle- and high-school grades) were more likely to graduate and go to college than their peers. In a September 2011 study of ACT results by the Illinois Policy Institute, 14 of the top 25 performing open-enrollment high schools, and 9 of the top 10, were charters.

Most of these high-achievers are run by the Noble Charter Network, including Pritzker College Prep, which was founded by Hyatt-hotel heiress Penny Pritzker, a longtime supporter of Emanuel and President Barack Obama. Several other operators have struggled. This is typical: a major variable in charter success is oversight of the school operators and especially the school "authorizers," groups that get state permission to create the schools, draw up their founding contracts -- the “charter” -- and oversee their boards. (A Bloomberg View editorial today has specific recommendations for regulating authorizers.)

The charter schools are at the heart of the Chicago strike. For the union, a big sticking point has been the school board's insistence that teacher assessments be used for merit pay and to make it easier to fire bad teachers. (This summer the city had to return a $35 million federal teacher-incentive grant because union officials wouldn't agree on an evaluation system.)

Rewarding good teachers with financial bonuses and increased freedom in the classroom is a central tenet of the charter movement. It's a concept that will likely have new appeal to Chicago parents missing work today and sitting at home with idle children.

(Tobin Harshaw writes editorials for Bloomberg View on education and national security. Follow him on Twitter.)