The use of the present perfect continuous emphasises the repeated work and/or constant state of working hard over a particular period. The emphasis is on the activity of working hard. This is different from the present perfect (simple), which would stress the completion or result of the work. The time period would be the same in both cases.

I’m not surprised he has failed that exam. <<== "he has failed" (a completed action) He has not been working hard recently. <<== "He has not been working hard" (negation of a repeated activity) Su. Ki. has given an excellent answer. The present perfect continuous emphasizes a repeated activity. For more details, English Grammar in Use by Raymond Murphy is an excellent book for self-study and general reference. There are PDFs floating on the net. 4th edition - p. 18. You can use the present perfect continous for actions repeated over a period of time. "Silvia is a very good tennis player. She's been playing since she was eight."

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@Samuel Thanks. I was for the "failed" but there was no such option in the test. The girl asked if she could use hasn't worked instead of hasn't been working. She could according to grammar books but she had to choose one option. I'm just curious if natives can explain the difference)) if they feel any))

I need more explanation of what you want, is that sentence from a test? I thought it was a pretty standard statement... the kid failed the exam. Maybe If you said “I’m not surprised he failed that exam, he hasn’t been working hard recently” that would sound a little more natural, but other then that I think the author is just trying to get across that someone failed a test.