Thanks a lot for the feedback. My name is Abhishek Fatehpuria and I'm also a cofounder with Homeroom.
Theres a couple reasons why we think we're better than piazza.
1) Our discussion software yields higher quality discussion by having a more steady stream and well organized posts.
2) We're releasing more features which enables even more collaboration and discussion. Piazza only goes as far as posts and answers. We are going to do a lot more very soon.
3) Our target market right now has actually been the K12 market. We find that the softwares in that space right now are not that good and its incredibly fragmented.
That being said, I use piazza in school and I love it, and we know its pretty entrenched already in the higher-ed not K12 market.
Please let us know if you have more questions/feedback