Precalculus and single-variable calculus courses are a critical early juncture for the success of science, technology, engineering, and mathematics (STEM) students in the United States (US). The default course structure is often a required three-term sequence of precalculus, differential calculus, and integral calculus. In this paper we analyse variations to this structure, the nature of such variations, their frequency across US universities, and how instructional approach and performance rates in those variations compare to those in the standard course offerings. We found that course variations are relatively common, and are primarily targeting students with more math-preparation, less math preparation, or those majoring in a specific discipline. We found that for less prepared students, who are typically at the highest risk of failing, course variations resulted in similar passing rates, essentially levelling the playing field for these students. Although we had conjectured that disruptions to the standard offering would allow for greater use of active learning strategies, no such difference was observed. Ways in which these course variations can redress systemic educational inequalities, opportunities for design improvement, and future research are discussed. [Cowritten with the Progress through Calculus Team.]