But does it really seem like that much of a stretch to say that a single high pressure multiple choice test is a worse indicator of ability than a larger number of lower pressure tests?
A larger number of lower pressure tests, as you refer to them, occur throughout the school year as students progress through studies on various topics.
I believe you are supporting a fad that has outlived any semblance of credibility, and serves only as a distraction from legitimate issues faced by educators. Then again, I'm 32 years old, so perhaps I'm too old to "get it." I will note that standardized testing was a key aspect of my primary schooling, and I distinctly recall being able to roughly predict how fellow students would perform on such tests by simply applying what I knew about their actual level of knowledge on any given subject. Yes, I was a "strange kid" who spent far more time in school libraries and public libraries than in classrooms, but the bulk of my classroom time was spent tutoring other students.
You are advised to research alternate sources (and cite them in the future) for further data.