Will Robertson, a 31-year-old English teacher, was appalled by a sharp change of policy at Corbett High School near Portland, Ore. In 2005, the school decided to require that every student take at least seven Advanced Placement courses, including his.

He sent the principal a well-reasoned, single-spaced, four-page memo attacking the plan. He thought it was bad for learning to force students to take such a difficult course. Many, he said, were not prepared for it. They needed more time to develop intellectual maturity. Failing the class “could be debilitating for years,” he said.

Three years later, he produced another memo, also well-reasoned and single-spaced. It explained why his first memo had been wrong. When I found the memos this year, I had never read such a candid account of a teacher’s intellectual journey. I devoted a paragraph to them in an earlier column about his school, then persuaded him to let me use his name and quote the memos at length here.

I would love to hear from other teachers who have had similar changes in thinking, in whatever direction. Maybe they started out liking a program such as AP, and then realized they were wrong. I have learned much from educators — Robertson included — who were willing to show how teaching is also a learning experience for them.

“We should strive to set expectations above what we believe students to be capable of,” he said in his original memo. “However, I am also concerned with and feel compassion for students who struggle. I do not relish the idea of alienating a large percentage of an AP class because they are simply unprepared to deal with the material.”

“I resent the assumption that what goes on in my regular English classes lacks rigor and does not prepare students for their futures,” he said. “We do not curtail opportunities for students not enrolled in AP courses. On the contrary, I have the rare opportunity in Corbett to deliver one-on-one instruction based on individual needs.”

Robertson was a conscientious and fair-minded educator. He gave the new policy a try. He pushed everyone to meet the AP demands. He alternated AP English Language and Composition with AP English Literature and Composition every other year. After three years, he concluded his students could raise their game. “After about a week of initial grumbling, students began to accept AP for Everyone as the norm,” he said. “When presented with new and challenging pursuits, most teenagers will discover that they appreciate the opportunity to develop.”

He had said in the first memo that students needed more time to develop intellectual maturity. After teaching everyone at the AP level for three years, he concluded that by the time average students arrive “in the 11th grade they are capable of reading and writing about complex materials. . . . Have we unconsciously designed the ‘regular’ 11th- and 12th-grade English curriculum to accommodate those who are unwilling to try hard? If so, why?”

By insisting on AP for all, he had said in the first memo, the school risked alienating a large percentage of students and setting them up for failure. “I thought that students would come to me in tears. Every time the phone rang, I was sure that it was a disgruntled parent ready to bemoan the ills of AP for All,” he said. What he got instead, he said, was “not a peep.”

Many teachers have told me of similar experiences, though not in such detail. Insight in such matters comes slowly and in many forms. Just last month, a former science teacher at a prominent private school told me he discovered after many years that he didn’t expect as much success from minorities as others, and that was bad for his teaching.

Robertson did his undergraduate work at the University of California at Santa Cruz and his graduate work at Portland State University. He taught at Corbett until he was 41. He then realized his dream of teaching abroad in Thailand before deciding, as some teachers do, to try being a manager, with more responsibility and more money.

Some teachers become principals or district officials. Robertson took over a small consumer electronics manufacturing company, Sonic Technology Products, that his father started. He felt he had outgrown teaching jobs he had. But he told me he remained proud of his classroom work helping students be even better than he at first thought they could be.