Everyone has an opinion on the firing of 241 District of Columbia teachers as a result of Schools Chancellor Michelle Rhee's Impact evaluation system. An additional 737 teachers, found "minimally effective," will be terminated if their performance doesn't improve within a year.

But this issue, like many others in education, is not a "black and white" one. I am not familiar with Impact, but the performance evaluations I saw in my 23 years with Fairfax County Public Schools were deeply flawed: by turns rigorous or pro forma, based on outside evaluations during the merit pay years, and based on principals' recommendations all the other years. There were rarely surprises: What the principal thought of you was clear right from the beginning, and the observation reports rarely ventured into new territory.

Much of the process was arbitrary. When FCPS first adopted pay for performance in the late 1980s, new teachers were not given high ratings under the belief that veteran teachers deserved the bonuses. The effect was that teachers first observed early in their careers were, a few years later, miraculously rated higher and bonus-worthy. That happened to me even though my teaching had not changed.

The process was divisive, as well. There was much anguish as some teachers were given extra money, and others not, causing resentment among colleagues and whispers of favoritism within schools. Before it got too ugly, Fairfax County dropped merit pay as too expensive. This defunct FCPS plan revealed many flaws in a well-intentioned effort at evaluation, some of them, no doubt, part of Impact.

What kids are reading This weekly column will look at lists of books kids are reading in various categories. Information on the books below came from Amazon.com's list of children's best-sellers. Books about teachers 1. My Teacher Likes to Say by Denise Brennan-Nelson (ages 4 to 8) 2. My Teacher Sleeps in School by Leatie Weiss (ages 4 to 8) 3. Teachers' Night Before Christmas by Steven Layne (ages 4 to 8) 4. Little Critter: The Best Teacher Ever by Mercer Mayer (ages 4 to 8) 5. The Teacher from the Black Lagoon by Mike Thaler and Jared Lee (ages 4 to 8) 6. My Teacher Is an Alien by Bruce Coville and Mick Wimmer (ages 9 to 12) 7. I Know an Old Teacher by Anne Bowen and Stephen Gammell (ages 4 to 8) 8. The Best Teacher in Second Grade by Katharine Kenah and Abby Carter (ages 4 to 8) 9. This is the Teacher by Rhonda Gowler Green and Mike Lester (ages 4 to 8) 10. Jake Drake, Teacher's Pet by Andrew Clements and Janet Pedersen (ages 4 to 8)

The insistence on full certification for all teachers is also a gray area. The commonwealth of Virginia granted me certification even though my background was in my discipline (a Ph.D. in English literature) rather than in education. They don't do that anymore, so someone with a Columbia University Ph.D. and teaching experience would not possess proper certification. Ask teachers where they learned to teach, and they'll almost always say they learned from their students and other teachers, not in an education course. Evaluations are never easy matters, so I am loath to label the recent firings either good or bad. I am sure many of the 241 teachers were not reaching their students, but I've never seen an evaluation system (except the highly regarded National Board for Professional Teaching Standards process), that was fair and objective in all cases.

Evaluations often get into trouble when they try to define good teaching. It's not about student scores, nor is it about how many courses teachers have taken, nor how many years they've been in the classroom. It's more intangible -- having to do with love of children and a passion for helping them move forward in ways that only begin with the curriculum.

Evaluation systems turn the complicated art of teaching into a simple, measurable formula, and my experience has shown they miss important nuances. There are shades of gray in every teacher's technique, shades that become black and white here. I will never trust personnel decisions based on a process less complete and intelligent than the individualized, non-principal-based one used to identify National Board Certified Teachers. Alas, that process is too expensive for public school districts, so flawed evaluation tools are all we have.

Erica Jacobs, whose column appears Wednesday, teaches at George Mason University. E-mail her at ">ejacob1@gmu.edu.