Los Angeles high school teacher Guillermo Mendieta is going on a hunger strike.

Not over salary, or benefits, or working hours. He's putting his passions where his mouth is over--of all things--mathematics, and the way it's taught in L.A. schools.

Specifically, Mendieta is trying to stop the Los Angeles Unified School District from giving up on a decade of reforms in math teaching. He and others feel these reforms have brought the power and pleasures of math to students formerly written off as hopelessly math-inept.

Many of these students are black or Latino. The rest are almost everyone else who didn't breeze through math in high school: Allergic to algebra. Terrified of trig. Catatonic over calculus.

These widespread aversions are side effects, many believe, of the drill method of math teaching, which is about as likable as the drill method of dentistry. As antidotes, reformers brought in everything from hands-on activities to art and games.

They added alternatives to the single-minded math track that forces students to march inexorably from algebra to geometry to pre-calculus, built bridges between various branches of math and even blazed trails from math to science, humanities, literature.

Back-to-basics advocates argue that while reforms might have made math more appetizing, they don't provide the kind of substance that leads to real competence. Appealing, perhaps, but junk food. This lack of competence, they say, shows up in the ever-dismal test scores of U.S. math students--particularly those in L.A.

To be sure, tests are invaluable as a tool to measure what students know and where they stand. But tests can't tell you everything.

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Consider that famous turn-of-the-century math student, the horse Clever Hans. When Hans' owner asked the horse to add, say, 3 plus 5, Hans pawed out the right answer. Hans couldn't do sums, of course, but he could read his owner's silent cues (perhaps no less of a feat).

Lest you think Clever Hans is a quaint historical oddity, the same phenomenon turns up today, even in the most amazing places--Harvard, for example. A documentary produced some years ago by Harvard and the Smithsonian Institution, called "A Private Universe," filmed newly minted Harvard graduates as they struggled to answer the question: Why is it warmer in summer than in winter? Most got it wrong.

All these students, one presumes, were above-average test-takers. Some had even studied astronomy. But like Hans, they had answers without understanding.

Math tests, in particular, tend to be timed--which rewards students who can solve problems quickly. This is a good, useful and sometimes important skill. But not always. "To most professional mathematicians, the focus on speed is crazy," says mathematician Keith Devlin, author of the forthcoming "The Math Gene" and dozens of other popular math books. "Most of the good mathematicians I know are very slow. All the tests really discover is whether you can do something fast."

Devlin and others worry that judging the success or failure of math teaching by test scores--especially timed tests--discourages students more than it helps teachers evaluate what they need.

His own daughter was left back in high school math for poor performance on tests. Given the time she needed in college, she went on to make straight A's. When Devlin wrote about his daughter in Focus, a publication of the Mathematical Assn. of America, he received hundreds of passionate letters recalling similar experiences.

Passion, of course, is something no test measures. And it's passion that is propelling Guillermo Mendieta to go without food for as long as it takes to make his singular appeal. He knows how it feels to be starved for the confidence that comes from being at home in the world of numbers, the pain of exclusion that dooms most children to a life of feeling inadequate--OK, let's just say it: stupid--in math.

To go through life feeling muddled by math, Mendieta understands, can be as impoverishing as going through life hungry for food.

So before the school district junks math reform, it needs to think hard about the way it measures success. The paths to mathematical literacy are many and varied. Depriving kids of the good feeling that comes from knowing a thing or two about numbers would be far worse than letting them eat a little cake.