Dozens? More like thousands. School districts tend to fall along city or county lines, and there are around 3000 local government units in the US. Cut that in half to guesstimate the number of school districts, and you’re still in the thousands order of magnitude.

Edit: There are 3142 “counties and county equivalents” in the US. See https://en.wikipedia.org/wiki/List_of_counties_by_U.S._state...