How much of a difference do passion projects leave on admissions?

Answered

Passion projects are really important for T20 admissions. I have never seen a HYPSM admit without at least one, significant passion project. Considering that you're a rising sophomore, it's the perfect time to get a project like that started, actually!

First of all, it's important to understand that there's no equation for starting a successful passion project, but I think there are a few things to consider with a passion project.

1) At least give it the appearance that you're not just doing it for college admissions. If the admissions officer feels like your entire project is just a sham to get into Harvard (and trust me, they have probably developed a really good intuition in terms of filtering those out) it'll lose it's impressiveness, and may even make your whole application seem disingenuous.

2) Make it about something you're actually passionate about. This has strong ties to the last point. For example, say you're a computer science guy. Don't just start a random organisation to help starving children in the Western Togo region (assuming you have no personal connection to the issue). Instead, teach underprivileged children how to code in your neighbourhood or something. That seems far more appropriate considering what your general academic profile will likely be.

3) Don't be a megalomaniac. You're in high school. Don't make your passion project some lofty goal like becoming a state contractor for curriculum development or something. Stay realistic with what you want to achieve.

4) Start small and aim for slow and steady expansion. Don't try to do too many/too complex things in the beginning, but rather to slowly expand the scope of your project as you gain more experience. To come back to the CompSci guy from point 2, once the "teaching kids how to code" thing takes off in his neighbourhood, he could create a formalised curriculum on how to teach underprivileged kids how to code. He then gets a few friends from his school to also teach the same curriculum to more pupils, expanding the scope of his operation.

5) Strive for formal recognition. Are you doing research project? Get your results published in a decent journal. Are you starting an organisation? Incorporate it as a 501(c)(3) non-profit. This will make your project seem more credible and more legitimate.

Be aware of the fact that that's a non-exhaustive list of general guidance in terms of passion projects (with a particular focus on organisations).