IMPROVING America’s schools is no easy task, but in recent years the school-reform movement has made great strides and there is growing agreement about what it takes to make a great school. The tired arguments of the past are finally being put to rest. Much as we would like to say that the key is something simple like charters, or smaller classes, or different testing, or fewer mediocre teachers, or more motivated parents, or less poverty, in fact there is no silver bullet. A system this stagnant requires changes on many levels.

The boffins at the Urban Education Institute (UEI) in Chicago have written an exemplary book on school improvement. They looked at 100 elementary schools that showed progress in attendance and test scores over a seven-year period, and 100 others that did not. They argue—with quantitative data—that five essential pillars are needed to build a great school. These are: effective school leadership, collaborative teachers (with committed staff and professional development), parent-community ties, a student-centered (and safe) learning climate with high expectations, and ambitious and demanding instruction.

The teachers in UEI's home city of Chicago are striking, leaving 350,000 children out of class. The unions say they only want the best outcome for the students. But this cannot be true. This is because their demands (to have a role in the hiring and firing of teachers and to weaken or delay plans for improved teacher assessment) essentially kick away at two of the UEI's five essential pillars for great schools.

For effective school leadership, the head teacher must be able to hire and fire teachers. (This, one might add, is hardly a revolutionary approach to the workplace.) Instead the union feels it must have some input, and that the most recently sacked teachers should be first in line for a job. Do any readers fancy trying to run a school, or any organisation, with the staff that you are told to hire rather than those you want? Neither do I.

The other reason teachers are on strike is that they don’t like teacher evaluations, and they really don't like them being linked to their pay (even though this works). You'll hear that the arguments are over the kind of tests that are used and the extent to which it determines pay. But the bottom line is that the union doesn't like any serious teacher evaluation and wants to delay it for as long as possible. Yet teacher evaluations linked to pay are coming; it is a national tidal wave.

The current evaluation system is so ineffective that that 99.7% of teachers are deemed satisfactory to distinguished. In other words, all of Chicago’s teachers are above average—despite the fact that four out of ten of the children they teach do not actually graduate from school. If that figure isn't mind-boggling enough, consider also that of every 100 first-year students who enter a public high school in Chicago, only about six will earn a bachelor's degree by the time they reach their mid-20s.

Karen Lewis, head of Chicago's teachers union, whined on Tuesday that there were too many factors beyond their control "such as poverty, exposure to violence, homelessness, hunger and other social issues beyond our control". Yet the Chicago Tribunepoints out that a federal study shows that poor inner-city kids in Boston, New York, Houston and other metro areas outperformed Chicago elementary students in maths and science. Moreover, the University of Chicago is able to run four public charter schools serving 1,700 students on the South Side of Chicago and have 100% of its 2012 class accepted to college.

In the last decade, 200,000 people have left Chicago. Today 150 of its schools are half empty. Families have fled the city's terrible schools and gone to the suburbs. And the city is desperate to reverse this trend. This is why it is safe to assume that the demands of the city are aligned with the needs of the students and parents. And the reason that demands of the unions are not aligned with the children is that about 100 schools need to close. Tim Knowles, director of the UEI, told "Chicago Tonight", a public-affairs television programme, earlier this week that this could mean about 5,000 teachers (or 20% of the union) losing their jobs. Of course the union wants to make sure it has a say in who gets rehired, regardless of whether this is best for the children. Of course the union does not like teacher evaluations; it weakens the union's ability to protect all their members. The unions are entitled to their opinion. And teachers are of course entitled to strike; it is an important right. But let us not perpetuate the myths of this strike. The union is thinking more of its members than the children its members are charged with teaching.