I’m going to pull @edragonfly 's post over here because it was very well written.
I now work with low-income, first-gen high school students through a 1:1 mentoring program. The program provides excellent training for college mentors like me and my advice to all UC applicants is to really spend a lot of time on your PIQs, starting the summer before senior year. Get feedback and iterate. This is the only way you can stand out since stats and activities (usually accomplished musician/athlete/club president) are so common these days. You need to be memorable and the best way is to choose the PIQ’s that showcase you the best and tell complementary stories about you. Also important is to strive for a balance of story-telling and reflection. The best PIQs are well-balanced between telling what happened and reflecting upon the event…what did you learn about yourself, the world and how did it shape or change you, your outlook and what you want to do in your future. If the essays are all story-telling or all reflection, they don’t showcase you as well as ones that are well balanced between story and reflection. Obviously, not going to help you or your student now, but if you have younger ones, you have more tools, knowledge and experience to help them. Not implying that your student did not have stellar PIQs, just advice to future students who hang out at CC forums.