Hey, we did a project on this in AP World History last year. Let me see what I can remember about it.
American students are 27th in math, 23 in reading, 28th in science, the the worst 1st world country in the world, iirc. However, we do excel in one area: our students are more cocky about their intelligence than anywhere else in the world.
Tha United States' education system has a few things that the other world envies - sports integrated into school, caring towards emotional wellness, and the best universities in the world. American education also focuses a lot on group work, something that many countries don't have, and this translates to a population much more able to work together, as well as allow for more creativity compared to students who spent their school time taking notes and memorizing.
But it all goes downhill from there. There are a bunch of problems with American education. The most important, I think, is teachers.
First of all, working a certain amount of years gives you tenure. Once you have tenure, you cannot be fired without a very lengthy procedure that most schools do not bother with. So these parasitic teachers continue to suck money from the system and retard the growth of their students. The vast majority of schools have a significant amount of these poisonous teachers. A bad teacher can teach half of what an average teacher can in a year. A good teacher can teach double of what an average teacher can teach in a year. Many students, taught by multiple years of awful teachers, end up too far behind to comprehend the material of high school, and drop out. The United States has one of the highest high school dropout rates of 1st world countries.
Secondly, teaching is a much more prestigious vocation around the world. In most of the top 10 countries, you need a master's degree in teaching (or maybe it's strongly encouraged, can't remember). In the United States, it's almost optional.
Third, American education is stagnant because there is no incentive for teachers for excelling. There is no incentive for innovation or improvement because teachers are paid, not on a merit-based system where a higher amount of success in their students results in higher pay, but with a flat salary that is increased the longer teachers are employed by the school. In other systems, teachers are encouraged to try new ideas and methods on teaching and share their successes with their colleagues. Here, teachers are rigidly bound to the curriculum and rarely deviate.
Lastly, the teacher's union makes all of this basically impossible to change. They throw fits whenever a teacher is fired, whenever higher requirement are needed. They felt so threatened by the concept of merit-based pay that they did not even put it to a vote. They pay large amounts of money to politicians to look the other way.
Also, the top country academically, Finland, does something really nice that America doesn't, and that is cater to students on an individual basis. Teachers take time for each student separately and help them to understand the material personally. In America, this isn't a a thing. Everything is standardized and people who don't mesh well with standardized testing are marked as failures. I...don't really remember if other countries do this. But Finland is awesome. They also don't have homework. Which I totally agree with.
Then there's the issue of how our universities are privately-owned and outrageously expensive, growing more expensive by the year, so that anyone who attempts them winds up with huge amounts of crippling debt. But we kinda focused on high schools, so I don't have as much to say about that.
Some of this is wrong because I'm mostly going by memory and casual google searches. Sorry.