Do you have citeable evidence that principals are facing lawsuits for using 'teacher recommendations' to either assign students to limited slots, or to discourage students from competing for those slots (e.g. tell students that a teacher recommendation is required, knowing that one group of students will see it as more of a bar to entry than another, resulting in a smaller proportion of that group even competing for the slot).

Because either of those actions are indistinguishable from using race as a factor in determining access to classes.