GreatSchools is simply the most awful company I have ever interviewed at. The lack of communication during the process is astounding! My advice would be to not even hit the apply button. Because if you do, then you will be sucked into this blackhole where you get a response every 3-4 weeks and the process will last months. It will end without you even knowing why you were rejected.
I applied through a recruiter. The process took 3 weeks. I interviewed at GreatSchools (Oakland, CA) in June 2017
Interview
Very thorough. There was a phone screen, a coding challenge, and then an extensive on-site interview that lasted the entire afternoon. It started with a review of your coding challenge, then some technical questions, then meeting the team, then a group code review, then a general discussion of your background with the team, then a challenge to develop a feature in their codebase in an hour while the team circulated watching over your shoulder while you worked.
At the end of the day, it was made clear that I should expect an offer. Then I never heard back. They didn't even have the common decency to follow up to tell me that after committing to and acing their rigorous interview process, a referral of a current employee jumped ahead and took the position. I only found out this is what happened when I hounded the recruiter who connected me to the job opportunity in the first place.
So bottom line is: the interview process is extensive but fair, however their communication practices are severely lacking, and there is a certain lack-of-ethical component that seems related as well.