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Although my first exposure to standards-based grading came from tutoring a high school student whose precalculus teacher used that grading scheme, I wonder whether the goals that college educators hope to achieve by adopting standards-based grading are at odds with the role the precalculus course is meant to play in the larger framework of college STEM education. For example, the goal of uniformity across sections as to what each letter grade implies about content mastery might preclude some of the integrative learning possibilities that fit naturally into a course at this level. What follows are my attempts to elaborate on two conflicting roles that the precalculus course might play, depending on the individual instructor's philosophy.
On the one hand, precalculus comes at a stage in the mathematics students' development that they can start to appreciate a wide variety of topics, from elementary number theory and proof techniques to non-commutative matrix algebra and the geometry of complex numbers. In this sense it can be treated more like a survey course, the last such overview of the mathematical landscape before they embark on a three-semester followup path that utilizes only a handful of core ideas.
On the other hand, precalculus can be viewed as the first course on a four-semester journey, only at the end of which are students allowed to take their recent mastery of multivariable calculus in whichever direction they fancy, having seen glimpses of the broader mathematical landscape along their calculus journey. An argument in favor of this role for precalculus is the existence of alternative survey courses or non-calculus foundation courses. A second argument for precalculus as an entry point rather than a capstone experience is the peculiar requirement that STEM calculus students satisfy the formal prerequisite of precalculus, rather than just the college algebra course that suffices for students in applied calculus.
My own preference is to treat the precalculus course as a capstone experience rather than a narrowing of focus (which the students will have plenty of time to do when they get to Calculus I). Because I expect the graduates of the prerequisite courses intermediate algebra and introductory trigonometry to retain some proficiency with the algebraic skills seen in those courses, I try to downplay the actual mechanics and emphasize instead the deeper connections that underlie the functions they're studying. For these purposes I introduce some calculus ideas informally, including limits at infinity, area accumulation functions, the binomial expansion, geometric series, and scaling arguments that anticipate the chain rule. None of the textbooks currently on the market are written with this capstone approach in mind, but some of the material in undergraduate "history of mathematics" textbooks can be used as supplements. The excellent text "Numbers and Geometry" by John Stillwell (and to a lesser extent, his other book on the history of mathematics) has a wealth of examples that the precalculus student might appreciate.
If a particular math department has strong consensus about which role the precalculus course should serve, then naturally the individual instructors should conform to that expectation so as not to confuse the students who seek help from peers in other sections. Trying to introduce standards-based grading in a department that treats precalculus as a capstone experience would fit awkwardly, while SBG might work perfectly well in a course that seeks only to develop the specific skills needed by the future calculus student.