American here:

About 20% of Americans are functionally illiterate, 2nd grade or worse reading and writing skills.

The average literacy level of Americans is between 5th and 6th grade… meaning the next 30% have the reading/writing skills of someone who only did elementary school.

These are numbers for adults 18 and up, by the way, not kids.

Almost every single person I’ve met who learned English as a second language… can speak it more fluently than most native English speakers I’ve known who grew up in America. More extensive vocabularies, better grammar, better spelling.