I agree that it's reasonable for teachers to not want to do more work. And I understand that creating tracks will separate students — but that doesn't require creating the perverse incentives you describe.

Teachers can simply be evaluated based on how their students do, relative to the students' prior performance. This wasn't a problem before 2014, when CA made GATE optional. Everyone understood that different teachers had different cohorts with different average abilities.

The teachers with lower-performing students weren't dinged because their students scored lower than the students in advanced classes. Instead, teachers could specialize in remedial, typical, or advanced learning.