The mayor's Partnership for Los Angeles Schools gave them math and literacy coaches, more feedback and the opportunity to watch their more effective peers, said Angela Bass, the group's former superintendent of instruction.
Bass acknowledged that it could take years for foundering instructors to improve, if they do at all. In the meantime, about 20 students a year will continue to sit through their classes.
"It's tragic," Bass said. "It means we've failed them."
Miko Dixon, the principal at Topeka Drive Elementary in Northridge, took a tougher approach. Upon starting the job in 2009, she said, she identified four highly ineffective teachers. One had decided, with the approval of the previous principal, to keep his second-graders as they moved to third grade, ensuring two years of poor teaching in a row.
"It's criminal," Dixon said. "If you get a bad teacher in second and third grade, you're doomed."
Dixon has begun trying to remove the four teachers, a painfully slow process in California. It's far more likely that they will feel the pressure and transfer to another school, she said.
"That's not right," Dixon said, "but it's reality."
For now, parents remain mostly in the dark.
Even the most involved mothers and fathers have little means of judging instructors other than through classroom visits and parking lot chatter. Others don't even have time for that.
Without reliable information, it comes down to trust. Which instructor a child gets is usually decided behind closed doors by principals and teachers, whose criteria vary widely.
"Mi niño, all his teachers are good," said Maura Merino, whose son Valentin Cruz was in the fifth-grade class of John Smith, the low-performing Broadous teacher, last school year. "He never had a problem. Everything is OK."
Merino said it's hard for her to tell the difference between teachers because she doesn't speak English. If she knew her son was assigned to a struggling teacher, "I wouldn't know what to do," she said, speaking in Spanish. "But I would try to get him to the best."
In a conversation after school one day, several Broadous teachers, including Aguilar and Smith, said parents should have the chance to see how teachers measure up.
They "might be more empowered to demand a good teacher," said teacher Eidy Hemmati. And it might keep teachers "on their toes a little bit more," Smith said.
But many others say it would be impossible to accommodate every parent's desire for the best teacher, and publicizing disparities would only turn one educator against the other.
Broadous Principal Stannis Steinbeck refused even to discuss the differences among her instructors, hinting at the tensions that might arise on staff.
"Our teachers think they're all effective," she said.
Times data analyst Sandra Poindexter contributed to this report.