Students will return this morning to public schools in New York City, a slow start that goes to the heart of what is wrong with the Department of Education’s “Children First” initiative.

Boys at parochial schools in the city donned their white shirts and ties, and the girls slipped on their plaid skirts, last Wednesday, giving them a three-day head start on their public-school compatriots.

Many of the surrounding suburban schools districts also welcomed their students back on Wednesday, some on Tuesday, and some even two weeks ago.

Summer vacation did end on time for city public school teachers, who have been back on the job since Tuesday, the day after Labor Day.

All city principals – who work a 12-month year – were back at their desks a week earlier. Rather than provide instruction for children these past few days, the system was following a “progressive” education precept: that the professional development of teachers takes precedence over the education of children.

There has always been a gap between the day teachers returned to work and the children arrived for their first day. But this year’s four-day chasm is unprecedented. At no time in recent memory have children started school so late by design.

This has not always been the attitude of the Bloomberg administration. The mayor, in negotiating the last UFT contract, gave teachers a significant pay increase tied to working an extra 20 minutes a day. The clear presumption was that this extra time was to provide additional instruction for students.

Back in July 2002, the mayor was reported to be livid after the chancellor at the time, Harold Levy, decided to use half of the additional time for professional development and the other half to provide remediation for only the lowest-performing students.

This took place just days after Mr. Bloomberg was given control of the schools. The mayor directed Dennis Walcott, the deputy mayor handling education matters, to read the riot act to Mr. Levy, who was replaced just days later by Joel Klein.

Within a month, the new chancellor put part of the mayor’s original vision of additional instructional time into place by adding two days to the school calendar for children, eliminating two previously scheduled days of teacher-training.

A month later, Mr. Klein announced that all schools would extend daily instruction time by at least 15 minutes, and in many cases by the full 20 extra minutes.

During those early, hopeful days of mayoral control, principals, teachers, and parents applauded the chancellor’s initiative.

“More instructional time for all children in the system offers them a better opportunity to achieve the high standards we have set for them,” Mr. Klein said. The New York Sun quoted a fifth grade teacher as saying: “There is never ever enough time in the school day to get all the work done.”

Within a year, Mr. Klein had backtracked to a position closer to that of the departed Mr. Levy, scaling back the extra instructional time by half. The deputy chancellor for teaching and learning, Diana Lam, restored the professional-development mandates so derided by the mayor just a year before.

Ms. Lam may be gone, but the direction in which she took the system has not changed. The “expanded” school day for children is now only 10 minutes longer, instead of the intended 20 minutes. The balance of the time has been loaded into 18 100-minute professional development sessions for their teachers.

These 1,800 minutes represent the equivalent of a full week of possible additional instruction lost to our children. Add to that the time lost last week, and you can see how students are being nickled and dimed.

Fifth-graders are coming back to some news. They, like pupils in the third grade, now must “pass” the end-of-year standardized tests in order to be promoted. “Passing” means attaining the barest competence in reading or math. If the results of the first year of the mayor’s “end to social promotion” are any indication, the fifth-graders have little to worry about. The same number of third-grade students was held back this year as last.

But at least the mayor has announced his new program at the beginning of the school year, avoiding the confusion and controversy that accompanied his initial social-promotion initiative.

A more productive strategy would have been to work downward to the earlier grades, where such intervention has greater potential to pay real dividends. Fifth grade is too late to turn around many failing students.

So, welcome back to school and year three of mayoral control, still very much a work in progress.