It's not as simple as it being 'covered' though, is it? Times tables were 'covered' endlessly when I was at primary school. I still didn't know them because they wouldn't stay in there.
I know we did percentages in school. It was many years ago, but I know we did it. I still can't work out percentages without a calculator (and I had to find out how to do that, because we weren't allowed to use them for percentages in school).
I don't really understand why my brain doesn't grasp it, but it wasn't because I wasn't taught how to do it.
And from an educational point of view, I don't really know what they could have done differently to help me understand.
Whilst I now know I have dyscalculia, because it wasn't diagnosed (or even recognised) when I was at school, I don't know what needs to be done differently to help people like me, for whom just 'covering' it isn't enough.
How many children sit in class just not getting it, like I did? What do teachers do with the kids who simply don't understand? It's not enough to just keep repeating something someone hasn't understood properly, but might be able to do, parrot fashion, in the moment.