How do you comment on rapid improvement in a student's performance? Sometimes, it can happen that a graduate student who is struggling on a project finally sees everything "click," and becomes far more productive. It might be due to a change in attitude, an improved work ethic, serendipitous success, or some combination of all of the above.

In writing recommendations, how do you comment on the student's rapid turnaround, without making the previous state of the work (in which the student was working, and clearly understood what needed to be done, but didn't have the results to show for it) seem like it was a weakness or liability on the part of the student. Given how real signs of weakness can cause problems for people reviewing the letters, how do you call attention to the fact that the student underwent such a startling transformation, while acknowledging the previous struggles and not harming the student's chances?
I agree with JeffE's comment -- this is an opportunity to show fantastic improvement, which looks great in a letter.  If the improvement really was because of "serendipitous success," it seems that it would be difficult to sustain, unless it happens that the groundbreaking work was so monumental that it is prize-worthy (and even then, chance favors only the prepared mind).

If I'm writing a positive letter (which is almost always the case--I'll try to convince a student that I'm not the correct person if I feel I won't be able to justify a strong letter), my goal is to convince the letter-reader that I'd hire/accept the person now, and why.  Something like the following might fit this case:


  I have been particularly impressed by X's recent work on her project, Nuclear Powered Time Travel via a Modified Consumer Vehicle.  Despite a frustrating set of circumstances that returned limited results in the early stages of the project, her hard work and persistence led to a breakthrough that she is currently preparing for submission to The Twin Paradox Journal, and will undoubtedly lead to further successful results.  Specifically, she was finally able to properly shield the flux-capacitor plutonium containment compartment in her design, reducing temporal errors by 99% and leading to far greater box office returns.


If the student's previous attitude, or struggles don't put her in a particularly good light, don't include them explicitly.  Again, it goes back to would I hire or accept the student now?  If you believe that by not including the specifics you're not being honest, then maybe you wouldn't feel comfortable with such a positive letter anyway.