So I work in academic research, and a high school student that worked with me this summer asked me for a letter of recommendation for his undergrad applications.
This student is incredibly intelligent and was able to do things during the summer that I never got to do as an undergrad. They learned quickly and was able to work independently after only a few weeks.
That being said, this student is also an archetypal high-school overachiever - excelling academically, in sports, and in other extracurriculars. The bad thing is that during the summer, they were competing in sports and doing a major service project, so sometimes they couldn't come in or could only work half a day. That being said, while the student was here they would be committed, sometimes staying over 8 hours if our experiments ran long. This kid was so tired from all their activities that sometimes they would fall asleep in their chair. Additionally, few samples, reagents, and experiments were ruined because this student had a major tendency to forget.
But in the end my overall impression was a positive one because their final results were useful and their lab presentation summarizing their work was impressive.
So I had planned to write a letter that is mostly positive, but include a mention that
"X is well rounded, excelling in academics, athletics, and community service. X did all of these while working in our lab, and although they showed great ability to manage their time effectively, I can't help but think with their potential and quality of work, that X could have achieved even more during this summer. It's not to say that they spread themselves too thin, but rather that I hope that while at _____, X will discover what truly interests them, and I have the confidence that once they find their priorities, that they will be extremely successful in their endeavors."
I could easily omit that and just include nothing but the positives, but it really nags at me because there was room for improvement.
So in short: is it okay to mention flaws/room for improvement in an otherwise positive letter of recommendation?