For example, if a third-grade student ranked in the 60th percentile among all district third-graders, he would be expected to rank similarly in fourth grade. If he fell to the 40th percentile, it would suggest that his teacher had not been very effective, at least for him. If he sprang into the 80th percentile, his teacher would appear to have been highly effective.
The approach, pioneered by economists in the 1970s, has only recently gained traction in education.
A small number of states and districts already use value-added scores to determine which teachers should be rewarded and which need help. This summer, one district took a harder line: Washington, D.C., schools Chancellor Michelle Rhee fired 26 teachers based in significant part on their poor value-added scores.
Prompted by federal education grants, California and several other states are now proposing to make value-added a significant component of teacher evaluations. If the money comes through, Los Angeles schools will have to rely on the data for at least 30% of a teacher's evaluation by 2013.
The Times found that the district could have acted far earlier. In the last decade, district researchers have sporadically used value-added analysis to evaluate charter schools and study after-school programs. Administrators balked at using the data to study individual teachers, however, despite encouragement from the district's own experts.
In a 2006 report, for instance, L.A. Unified researchers concluded that the approach was "feasible and valid" and held "great promise" for improving instruction. But district officials did not take action, fearful of picking a fight with the teachers union in the midst of contract negotiations, according to former district officials.
In an interview last week, A.J. Duffy, president of United Teachers Los Angeles, was adamant that value-added should not be used to evaluate teachers, citing concerns about its reliance on test scores and its tendency to encourage "teaching to the test." But Duffy said the data could provide useful feedback.
"I'm not opposed to standardized tests as one means to helping teachers look at what's happening in their classrooms," he said.
Supt. Ramon C. Cortines, who was appointed in late 2008 and plans to retire in the spring, acknowledged that the district could have done more with value-added analysis but was focused on other ways of improving instruction, as well as with staying solvent.
"We have better data than anyone else in the nation — we just don't use it well," he said. "I think it's the next step. It has to be done."
A task force created by the Los Angeles school board to promote teacher effectiveness raised the issue in April, urging the use of value-added scores as one measure of performance.
The task force chairman, Ted Mitchell, said the changes were long overdue.
"I think it's simply a failure of will," said Mitchell, who also heads the State Board of Education.
'Don't be a robot!'
Even at Third Street Elementary in Hancock Park, one of the most well-regarded schools in the district, Karen Caruso stands out for her dedication and professional accomplishments.
A teacher since 1984, she was one of the first in the district to be certified by the National Board for Professional Teaching Standards. In her spare time, she attends professional development workshops and teaches future teachers at UCLA.
She leads her school's teacher reading circle. In her purse last spring, she carried a book called "Strategies for Effective Teaching."
Third Street Principal Suzie Oh described Caruso as one of her most effective teachers.