By Christopher Paslay

Michelle Rhee, the former Washington public schools chief whose draconian management style got her forced out, recently paid a visit to Simon Gratz High School in Philadelphia. Her main order of business was to push her school reform agenda, including a direct assault on Pennsylvania's "last in, first out," or LIFO, rule for teacher layoffs.

Rhee insisted that LIFO is getting rid of our best teachers, arguing that layoffs should be based on job performance instead of seniority. In an Inquirer commentary, Rhee cited an Urban Institute study to support her view that scrapping LIFO is a matter of "common sense."

A closer look at the study Rhee relies on is revealing. Titled "Teacher Layoffs: An Empirical Illustration of Seniority vs. Measures of Effectiveness," it isn't even based on real teacher layoffs. Rather, it employs a simulation. The authors write that they used "data from New York City to simulate the differential effects of layoffs determined by seniority and by value-added measures of teacher effectiveness." In layman's terms, it's pure conjecture.

The authors do admit, however, that first-year teachers are generally ineffective, and that it takes a teacher an average of five or more years to become skilled. This is not surprising: New teachers tend to struggle with classroom management, they lack experience and objectivity, and they have yet to perfect their instruction methods.

Rhee's claim that LIFO is getting rid of our best teachers is in fact based on exceptions, not the rule. We may in isolated cases lose a potentially great teacher by conducting layoffs on the basis of seniority, but ignoring teachers' years of experience would do more damage to the teaching profession and to students.

Policymakers who want to ignore seniority in favor of efficacy have to address some other issues. For instance, there would have to be a proven, reliable way to measure teachers' effectiveness, and it would have to account for variables that affect student achievement, such as poverty and parenting.

Even if we could agree on such a rating system, difficult questions about money, politics, and turnover remain. If all the teachers in a particular school are rated effective, what's to stop a principal from balancing the budget by laying off the highest-paid teachers and keeping the least expensive ones? What would protect experienced teachers from politically motivated reprisals if they encourage their students to think critically about school reform and other public policies? And what will keep the new teachers we're relying on from constantly leaving the system? In my 15 years with the Philadelphia School District, I've watched at least a dozen Teach for America educators leave after fulfilling their two-year contracts, off to use their urban teaching experience as resumé padding.

"Last in, first out" isn't causing us to lose our best teachers. Far from it. Ending seniority-based layoffs might occasionally save a young talent. But it would also harm teacher morale, leave experienced teachers vulnerable to budget cuts and experimental reforms, and populate our schools with inexperienced teachers who are likely to leave.

Christopher Paslay is a Philadelphia schoolteacher and the author of "The Village Proposal" (Rowman & Littlefield). His blog, "Chalk and Talk," is at http://chalkandtalk.wordpress.com.