A recent article from Education Policy Analysis Archives features some interesting research exploring teachers' ability to make themselves unqualified--after they're already highly qualified.

Sound strange? Penelope Earley and David Brazer have hit upon a newly documented but unsurprising phenomenon: teachers intentionally removing endorsements from their teaching licenses. (Endorsements specify the subject areas and grade levels that a teacher is authorized to teach.) They suggest that this abdication of knowledge may be increasing as pressure mounts for schools to have a highly qualified teacher in every classroom.

Teachers qualified to teach, for example, special education, may decide for one reason or another they don't want to teach that assignment any longer. Depending on state policy--which varies widely across the country--they may be able to simply pre-empt a district's teaching assignment by removing the special education endorsement from their license. Nine out of 26 state certification officials reported that special education was the endorsement teachers most commonly requested for removal.