My favorite teacher, Al Ladendorff, died March 20 at the age of 93. At Hillsdale High School in San Mateo, Calif., he was known as “Big Al.” Educators like him enhance our lives, for reasons not always in sync with what policymakers are doing to try to improve teaching.

The guarantees of highly qualified teachers for all students in the federal No Child Left Behind law are a sham. The law gives states that responsibility, but they have done little to inspire the intelligence, imagination and perseverance that so impressed me about Ladendorff. The replacement for that law, now being fashioned in Congress, does no better.

Also, the current fad for motivating teachers with individual ratings based on test scores is not working. Raising educator quality is always a heavy lift, politicians seem to say, so why bother?

Yet we know what we like about our best teachers. Why can’t we figure out ways to encourage such qualities in more classrooms?

My U.S. history class could have been a disaster. It was stuffed with nearly 40 students, as were many classes in the 1960s. The state-sanctioned textbook was dull. The class convened after lunch, when a lot of us would have preferred a snooze. But the minute our tall, angular and bespectacled teacher strode in, we could feel the electricity.

What I found most exciting about Ladendorff was that he encouraged us to think for ourselves, many years before “critical thinking” became a fashionable bit of edspeak. He did things I had never seen before, such as encouraging us to criticize the textbook.

For an argumentative type like me, this was mischievous fun. I wrote an essay noting the textbook’s long discussions of agriculture bills and their political consequences. Why was the book bothering with that stuff when just 5 percent of the population lived on farms? The real America, I said, was in rapidly expanding suburbs such as San Mateo. The essay had many juvenile flaws, but it was a big step for me.

Ladendorff was famous for his challenging exam questions, such as “Fair trade laws are unfair. Disagree.” He conducted some government and history classes in the school’s little theater, confronting 100 adolescents at a time. He was funny but also quick to stifle signs of inattention. My classmate Bob Padgett, who later became a physician, remembered him as a “superb lecturer and challenge provider.” He also was the faculty adviser to the yearbook and the student store.

Padgett and his friend Don Leydig, who later became Hillsdale’s most innovative principal, teamed up to tackle a typical Ladendorff project: “Pose a change in our federal system of government that, if included in the original framing of the Constitution, would have resulted in consequences more favorable to the country. Illustrate with two examples demonstrating how this change would have accomplished that goal.” Padgett remembered feeling intrigued and excited, even if their detailed argument for balancing the budget every year had big holes.

Maureen Wilbur, from the class just behind ours, went on to teach math for 30 years. She told me Ladendorff was “the most influential person in my life.” She loved his reminders to “dig deep.”

Ladendorff puzzled and upset some students. One girl in my class called him a communist, to which he responded with a laugh. His personal politics — never revealed to us — were probably in the other direction. He liked shaking things up. He knew unpredictability helped engage teenagers.

I had other great teachers, such as Mike Callahan, John Glancy and Geraldine Palazzi. Ladendorff was less smooth, but that was not necessarily a bad thing.

Teachers do best when they have a deep love and knowledge of their subject and of children, and a principal who encourages them on bad days and praises them on good ones. There must be some way for schools to hire more people like that, with teachers like Al Ladendorff as an inspiration.