Generalizations about American education are difficult to get correct in my opinion. America is very diverse, and very accommodating to people of all backgrounds. When I graduated from a PhD program I had possibilities of teaching in Oregon, New York, North Carolina, and Georgia. By then I had taught in Utah, and Washington, (and later taught in North Carolina). I chose Georgia because it was near my home where my aged mother lived, and they offered me what sounded at the time like a better position. I was stunned by the low level of preparation of my students there, compared to those in Washington and Utah, but if I had chosen a position say at Columbia in New York, assuming it had materialized, I might now be raving about the high level of the stiudents' preparation.
I don't know much about Belgium but I have recently read some studies about the different levels of high school programs available and not all (BSO?) are academically oriented. Moreover it is not clear that immigrants, even second generation ones, achieve the same level of academic progress there as do native born citizens and their children. In the US we sort of throw everybody in the same classroom, often until college, and regardless of interest or natural bent, and the results admittedly are quite mixed.
I suspect we in the US have much to learn from many other more successful countries, but we may have perhaps different challenges. One person who has excelled at helping students who were failing begin to succeed is Uri Treisman, Reading his essays has given me some insight as to maybe why I failed so miserably in my first attempt at college.
I went from a weak high school background in the southern US to a strong college in the north. I was used to being the best and being surrounded by low achieving peers. So I dismissed all attempts by the school to offer tutoring and help, and avoided studying together with my fellows. This was disastrous in a college where the other students were actually much stronger than I was and could have helped me enormously. The good news was that the college was used to this phenomenon and did not give up on me and other such strugglers right away, but gave us a second chance.