"They are not learning much."
Translation:Ili ne multe lernas.
On this course, sometimes the "correct" answer given is not helpful for the current level of understanding people practicing this skill possess. I made a silly mistake and it gave me the same "correct" answer I believe you received: "Ili ne estas lernantaj multe." I do think that is correct, but so is "Ili ne lernas multe."
I think you are asking basically the same I am wondering about:
Does the English sentence mean that they don't learn about much things, or they don't spend much of their time for studying? I guess, it can mean either. I'm not native EN speaker btw. So in EO it is possible to express this slight difference, right?