Is plunge the right word? I don't know. But in July 2013, first-time California law graduates passed at a 76% rate. First timers from out-of-state passed at a 64% rate. This July, California grads passed at a 69% rate and out-of-staters passed at a 60% rate.
We know there have been declines in several jurisdictions. We also know the National Conference of Bar Examiners takes the position that the decline in multistate scores results from a group of students that is "less able" than prior test-takers. Of course, there is the question of the massive exam screw-up that occurred thanks to Examsoft. But Examsoft says that the decline occurred in jurisdictions that don't use the software.
As David Frakt has noted, law schools that accept students with weaker predictors can be consequential. I'm not certain that what we're seeing with these declines is one of those consequences, but it seems a real possibility.,