I saw the D.C. schools headline in The Post, “600 instructors could be fired in July.” Here we go again, I said.

Summer is often a bad time for urban school districts, as officials fill teacher openings too late to get the best candidates. If the D.C. schools are waiting until July to see whether the new teacher evaluation system is going to cost 600 teachers their jobs for being “minimally effective,” that means their best possible replacements will already have been hired by other districts.

I learned this in 2003 through a report from the New Teacher Project, “Missed Opportunities: How We Keep High-Quality Teachers Out of Urban Classrooms .”

The report, written by Jessica Levin and Meredith Quinn, said: “High-quality teacher candidates regularly apply in large numbers to teach in hard-to-staff districts. The problem is, they do not get hired. The failure of many large urban districts to make job offers to new teachers until July or August is largely to blame for this problem.”

Why were urban districts so late? The report revealed three troubling practices: Teachers could without penalty wait until summer to reveal that they were leaving; existing teachers had first call on openings before new teachers could be hired; and budget decision delays left principals uncertain whether they had money for new hires.

The prospect of 600 dismissals in July seems part of the same malady. That struck me as odd, since D.C. Schools Chancellor Kaya Henderson and her predecessor, Michelle A. Rhee, for several years ran the New Teacher Project, the nonprofit recruiting and training organization that published that 2003 report.

Tim Daly, president of the New Teacher Project, told me that the delayed hiring issue was one of Henderson’s specialties, particularly since she had been the project’s manager of hiring for D.C. schools. “There is no one who knows this better than she does,” Daly said.

So I asked her.

Henderson had much to say about what she and her team have done to ensure that the D.C. schools never again lose the end-of-school-year hiring competition by being too slow.

Teachers no longer wait until summer to announce their departures. “The vast majority of vacancy notifications happen before April 1,” Henderson said. Veteran teachers can’t stand in the way of new hires. “The transfer requirements formerly in place through the WTU [Washington Teachers’ Union] contract that guaranteed late hiring of new applicants no longer exist,” the chancellor said.

Principals know how many slots they can fill. “Budget and forecasting are done early enough, and informed by data, to provide reliable information about where our vacancies will be,” she said.

It helps, Henderson said, that the new D.C. teacher contract promises teachers more money than competing districts. The teachers most likely to shine in class also like the seriousness with which they are interviewed and tested, such as the requirement that they be observed teaching a class with real students.

That makes sense. But won’t the lingering taint of the District’s bad old reputation and the controversy over its new teacher evaluation system still hurt when Fairfax County makes offers to the best D.C. prospects? Henderson says no. “The principals I’ve spoken with are thrilled by the caliber of candidates that are available to them,” she said. “We are no longer in a position where we elect to keep a low-quality teacher just because we are fearful about our options.”

We shall see. If 600 teachers are eligible for dismissal, and significant numbers are kept anyway by D.C. principals who don’t like the alternatives, that would be a blow to the new system. But Henderson is not worried, and I have to admit she appears to understand the ins and outs of hiring teachers for city schools better than anyone who has ever done it.