To differentiate instruction means to provide a different learning experience for every individual student in the class. Perhaps there is a student who is just learning English in your class. And perhaps that student sits next to another who wants to have an in-depth discussion about Shakespeare. Should these two students prove difficult to teach at once, a normal person might consider what the root problem is -- that they shouldn't be in the same class. But the wise education bureaucrat knows that any problem here must be the teacher's -- he must not have differentiated his instruction enough.Not to worry, it's entirely possible to teach "algebra" (however a non-math person wants to define "algebra") to someone who doesn't understand fractions.
Hat tip to Joanne for the link above.