Differentiated instruction (sometimes referred to as differentiated learning) involves providing students with different avenues to acquiring content; to processing, constructing, or making sense of ideas; and to developing teaching materials so that all students within a classroom can learn effectively, regardless of differences in ability. Wikipedia
When I was school librarian back when the earth was still cooling, teachers on a pretty regular basis would send kids to library with little notes. The notes usually read something like, "Mildred* has finished the story in the reading series. Can you find something more for her to read?" or "Can you find Philbert some materials on doing an astonomy project?"
Phil's and Mil's teachers were "differentiating instruction" even before the term was invented. Most teachers I knew and worked with tried to find suitable materials and activities for all kids, but especially those on the very high and low end of the ability spectrum. And where were those materials? In the school library's deliberately built collections of books on a wide range of reading abilities and on a wide range of topics.
Today we have lots of test data about individual students in schools (which has yet to be proven more accurate than gut instinct/observation of experienced teachers) that can be used to match resources with abilities. And someday diagnostic software may expedite and broaden the teacher's ability to match every child with specific online resources.
But until then, the library is ready, willing and able to help with both print and online materials and expertise.
* In all the years I've taught, I don't remember ever having students name Phibert or Mildred.