here is a fabulous package! I teach with here() exclusively now, in part because it makes it easy to solve issues where data and .Rmd files are stored in different sub-directories of the same project:
Using here("data", "data.csv") gets students easily around any issues with constructing file paths.
This in itself is the other reason I like teaching with here() - my students, few of whom have a cs background, really struggle with file paths. The way that here() forces you to specify each layer of a folder hierarchy as a string seems to help them develop a sense of the anatomy of their projects in a way that specifying paths as a single string does not.