How much do good teachers matter? Quite a bit, three Harvard and Columbia researchers concluded in a paper released last month.

The study, which tracked a million schoolchildren from fourth grade to adulthood, found that teachers who boosted their students’ scores on standardized tests also made lasting differences to their lives. Students with highly effective elementary- and middle-school teachers were more likely to go to college, had lower teenage pregnancy rates and earned more as adults, the study concluded.

The study comes as the state and city are wrestling with the teachers’ unions over a proposed system of teacher evaluations, which would assess teachers in part on how their students perform on standardized tests. In response, SchoolBook asked readers, “Do test scores indicate teacher effectiveness?”

Readers were divided. “Good teachers make a difference,” wrote Eunice Flanders, who identified herself as a teacher with more than 20 years of experience. “It is not rocket science.”

But Ms. Flanders worried that the study did not take into account “the huge number of factors” that affect students’ ability to learn, like divorce, hunger and chemical imbalances in the brain.

“It impacts the teacher,” she wrote, "no matter how good,” as well as other students in class.

Many readers seemed concerned that evaluation systems would overemphasize competition among students and between teachers. One reader, Adam Grumbach, wrote:

Beware the model of "competition" when applied to education. Would you like to see schools compete for students the way laundry detergents do for customers? Do you want to see school advertisements criticizing their "competitors" as less effective?

Other readers thought more competition might be a good thing.

“I’m sympathetic to the teachers who argue that you can’t measure the intangibles or that it pits teachers against one another,” Stephen Heras wrote. But “learning is a competition, life is a competition, and we need to just focus ruthlessly on what matters, which is getting the kids prepared, not whether the grown ups in the room are feeling unfairly judged.”

The idea of a teacher evaluation system partially based on standardized testing data invites criticism of the tests themselves, of course, and readers came up with plenty. Deborah Orr, a New York parent, said she had seen the State English Language Arts standardized test and was “incredulous that they would be used to determine a teacher's worth.” She added:

One year, my child received a perfect score on her ELA test and a mid-level 3 the next. This discrepancy did not correspond to the quality of her writing pieces and other schoolwork in that period, and it would be unfair to blame the fluctuation on any factor beyond the test itself. I've heard similar reports from other parents. The tests are simply too inconsistent as designed -- they may be a useful gauge for at-risk kids, but their margin of error is too wide to allow them much impact in teacher evaluations.

One reader, Michael Rosenthal, emphasized the practical problems faced by cities that have implemented evaluation systems, like Washington and Houston:

Look at the rampant cheating in DC where they instituted this new system. Imagine how much goes undetected. Next imagine how "ineffective" the teachers who have integrity look compared to those who cheat to keep their paychecks.

Mr. Grumbach, the reader concerned about competition, also criticized the approach used in the study to measure teachers’ effectiveness, known as the “value-added” method. He cited a Washington Post blog post in which John Ewing, a mathematician and the president of Math for America, a non-profit organization, criticizes the math behind the value-added approach.

But critiques of the study’s methodology didn’t hold water with Jack Pierce. “Of course, no system is perfect,” he wrote. “But to decry the analysis and say it has no value is incorrect.”

What are your thoughts about testing and teacher effectiveness? Join the discussion on SchoolBook, and add your voice to the conversation.