Just out of interest, what happens to a child in the US school system who simply isn't very bright, and incapable of getting good grades?
Depends - on lots of things. With the standardized statewide testing in Virginia being such a big thing, and school accreditation depending on pass rates, the schools have come up with creative ways to offer tutoring, study buddies, get parent volunteers to help, lots of other things. Generally kids are grouped into more academically-focused, advanced classes or basic classes depending on their grades and skills.
Kids with mental limitations because of Down's syndrome, other problems are put into special education track and take classes on their level. Kids with learning disabilities should ideally receive help for their particular problem, and in my state they have "IEP" - Individual Education Plan - that addresses this and is revised annually. Lots of school systems still do have a vocational- technical education track. I live in a rural county, the schools participate with the vo-tech center in nearby city and kids in those courses get bussed to vo-tech center. Some kids drop out for various reasons and later get a GED - General Equivalency Diploma - equivalent to high school degree.
Some parents home-school because the regimented approach or environment in the school is not the most optimal for their child's learning style. There is a large amount of home-schoolers in my area and they have a regional home-school graduation every year in nearby city. There are private schools that may charge varying tuition, and classes often are smaller and there is more individualized attention.
My old college roommate actually dropped out of high school because of some mental health issues - depression mostly, it was a loooong story - and later took the GED exam, passed it perfectly, went on to college and graduate work which she did successfully.
I only know details about Virginia: Just about everyone with the interest has the opportunity to attend community college, usually a two-year course of study, and less expensive than traditional four year college or university. Most credits transfer to four-year colleges.
There are still options for people who just don't do well in school. Like horses, animals, growning things? You can work in a nursery or maybe work and live on a farm. Like old people? Many nursing home or home health agencies offer Certified Nurse Assistant courses, tuition paid if you agree to work for the agency for a certain period of time. Can you drive? Lots of places need truck or van drivers. Coordinated, good with your hands? Work construction. Like health care but grades bad? Take an Emergency Medical Technician course, you can work for ambulance company or Emergency services. My husband's uncle started his own janitorial business right after he got out of the army in the 50s. He worked hard, when he retired he sold the company for millions and lives in an ocean-front condo now.
Like others have said, the grades don't matter as much as the interests, drive, ambition, and desire to succeed after school.
Joy in Virginia