In New York, where I grew up, elementary school was always grades K–5. But I just found out that there are elementary schools (grades K–2) and middle schools (grades 3-5) in a handful of these communities. Additionally, a few private preschools offer classes up to the second grade, and a private school that serves students in grades K–12 views the third grade as the primary admission point.
I wonder if this is a relic from the past, a fad that failed to catch on everywhere, or just a way to deal with congestion? I searched Google for it, but I did not discover many results.