The city schools are likely to be heaped with praise tomorrow when Schools Chancellor Joel Klein announces this year’s progress report grades. But a dearth of low grades could actually turn out to be a double-edged sword for Klein.

When the progress report initiative was first announced, Klein said the grades would be used to determine which schools to close. This year, if the chancellor decides to close more schools, he could find himself in the position of arguing that his own accountability system did not accurately reflect a school’s shortcomings.

The grades are also sure to add to the scrutiny currently being given to the test scores that account for most of each school’s grade. The vast majority of a school’s progress report grade — 85 percent — depends on its students’ scores on state math and reading tests, with the bulk of that based on how much each student’s scores increased since 2008. (The remaining 15 percent of each score is based on attendance data and the results of surveys given to parents, teachers, and students.)

Under this formula, this year’s citywide jump in test scores could give rise to a significant jump in progress report grades. Indeed, we’ve heard from several sources that most elementary and middle schools are getting very high grades, and only a handful are getting failing grades. Last year, nearly 70 elementary and middle schools got D’s or F’s last year, and 79 percent got an A or a B.

But several recent studies have suggested that the state tests have grown easier to pass. On top of that, scholars have argued that the progress reports’ formula is not statistically sound. The formula has also delivered results in the past that contradict widely held perceptions: Some low-performing schools have received high grades, while other schools that are considered highly desirable got low ones.

Not every school will receive a progress report tomorrow. High school grades, which incorporate August graduation data, won’t come out until at least next month, according to Andrew Jacob, a department spokesman. Last year, high school grades were released in mid-November, just weeks before eighth-graders’ high school choices were due. The grades will come out earlier this year, Jacob said.

And the department’s new “parent-friendly” version of the reports, which showcase a stripped-down set of numbers, also won’t be ready tomorrow, Jacob said. Those reports, developed in response to criticism that the original reports were too complicated for the average parent to understand, will come out before parent-teacher conferences later this fall, he said. The first set of parent-teacher conferences, for high schools, happens at the end of October.