The article, The path not taken: How does school organization affect eighth-grade achievement?, explores the relationship between grade configuration and student academic outcomes. The researchers find that K-8 and K-4, 5-8 configurations yield comparable performance outcomes for students by the time they reach eighth grade, and that these outcomes are higher than for students who attend schools with other configurations (K-5, K-6, etc).
The authors also identify, empirically, reasons that K-8 and K-4, 5-8 schools may yield these higher outcomes; students change schools less frequently, students change schools at an earlier grade, such schools tend to have smaller within-school cohorts, and finally, there is greater stability in students’ peer cohorts, as fewer schools feed into one another.
Some important quotes from this work: “We find that the K-4 to 5-8 grade span path and the K-8 schools have positive effects on students’ performance gains relative to other paths” (pp. 295); "the more time a student spends in the school immediately attended before high school, the higher the student’s achievement gains by eighth grade, all else equal" (pp. 307); "Regardless of the number of schools attended, moving in fifth grade is the least disruptive and is not statistically different from attending only one school" (pp. 307).
Full article is linked below.