Will Carington, works for Noodle
Based on what I can see on the Vienna Elementary School website, it doesn't look like this school uses PowerSchool. According to the Parent/Student Handbook, teachers use a program called Blackboard for communication with parents and students. To access Blackboard, click the link that says "24/7 Learning (Blackboard)" at the top of the Vienna Elementary School homepage.
For more information about how to access your child's grades, etc., my advice would be to contact Vienna Elementary School directly at 703-937-6000. Additional contact information is also available on the school's Staff Directory page.
Hope this helps!