Not in the US but I recently helped my niece in math (7th grade) remotely since they now do fractions and also negative numbers. When I tested if she could calculate a random sum with unequal denominators she tried to add them up like someone who never saw fractions before. Also the school teaching sounds like chaos, classes are split and they apparently didn't even have an opportunity to go through the test in class together. My sister is worried since her grades dropped this year and considers putting her into another school because other subjects aren't great either. Luckily she's now going to in-person tutoring.