The NWEA (think MAP testing folks) offers some data on student learning during the pandemic. The general summary – not too bad. Students taking the exam (an important consideration) scored a bit lower in math, but at about the same level as usual in reading. This outcome is an improvement over what had been predicted by such agencies as Stanford’s Center for Research on Outcomes.
This makes perfect sense to me. Reading is a skill area in which explanations for how it is done are extremely difficult to generate. You can tell if a student comprehends, but telling them how to go about comprehending is difficult. Time engaged and encouragement are important. Math lends itself more to feedback and demonstration. The assistance one might experience in a classroom is not as easy to deliver online.
Issues of participation and access are distinct from the success of what available access can produce and there are obvious concerns here.