In the book "English Grammar in Use" (Murphy Raymond), I encountered the following example when talking about present perfect tense:
John hasn't studied very well this term.
and explains the use of present perfect simple tense as follows:
We use the present perfect tense when the period is not finished at the time of speaking
I, then, applied this rule to the example above which led me to think that the unfinished period here is this term. The speaker might be saying this fact before the end of the term.
However, the next units compare these two tenses and say:
PP Continuous: We are interested in the action. It does not matter whether something has been finished or not.
PP Simple: This time, the important thing is that something has been finished. We are interested in the result of the action, not in the action itself.
Having read this, I started confusing. The above example used the present perfect simple tense even if we do not know whether John has changed and started studying well for the rest of the term. So, in the example, we do not seem to be interested whether the action has been finished or not (as PP Continuous was said to be used in this case).
Would not it be, then, PP Continuous as
John hasn't been studying very well this term.