GMAT Sentence Correction (SC) | Re: teacher and students

Why is E not an correct option here?
I was confused between A and E, but then discarded E because :

e) for a method to motivate her failings students, the teacherhad attempted to implement a different teaching method every four weeks butwas always obtaining the same student performance

I was not convinced that this is correct usage because there is no reason to show this time sequence, since it is an obv sequence, and usage of progressive tense is not proper.

sayantanc2k please help

thanks
...

---