PowerSchool has been a great resource for our high school students. I can post announcements, update students, or give directions. I can also download materials for students to use (documetns), whether that be classwork, larger projects or review videos. This has been a very good tool for distruptions in the school calendar from snow days to our current situation.
One area I have not had any experience is the assessment portion of PowerSchool, but some of my coleagues have.
I have used assessments, but not to it's full potential. I use it for multiple choice and matching assessments. It's great because the grades go straight into the gradebook and the program checks the quizzes for you! You can copy the assessment and change it for the following year as well. I usually have a quiz open for a full week so students can do it on their own time and not take time out of class. I give them 3 attempts and you can set it to take the score of their best attempt.