It's not a secret that the system of education differs much from country to country. Recently I came from Ukraine to the USA and my elder son went to high school here, in California. So, my son and I, as his mom, discovered a lot of interesting things about American high school not from books, but from real life. Is American or European school harder? Is American education better that European? I will try to look into these questions using information I know, plus experience of my son's friends and their parents who moved to Europe and started high school there.
1. Class System
The first drastic difference that is easy to spot is the class system in the U.S. and Europe. In the U.S. each student has his own individual schedule, and the student may have English, for example, with one group of students and Math with the other group. This happens because the student may have different level of knowledge at different subjects and will attend the class with the group of students of the same level. In Europe all the students in a group have the same schedule of classes and attend the same classes.
In the U.S. classrooms are assigned to teachers while in Europe rooms are assigned to students.
2. Optional Subjects
American high school students have a list of subjects they can choose while European students don't have such option in the 9th and 10th grades. Of course, some courses are required for everyone, and include the English language, Math, Science, PE and some others. Only students of the 11th and 12th grades in Europe can choose some of the subject. In America all high school students may choose electives.

3. Sports Teams
In the U.S. sports teams are linked to schools and all schools have different teams, such as baseball, basketball, football, and others.
In Europe sports is outside schools and students can do sports in different state or private sports clubs which are not run by schools.
4. Getting Enrolled to School
Students in Europe get to high school depending on the exams they take in the 8th grade. The exam results determine what type of school the student will attend after the 8th grade. In the U.S. students are enrolled to high school within the school district they live in. Each residential area has a list of schools that students living there are supposed to attend.

5. Student Lockers
Every student in the U.S. has a locker that is outside the classroom, but in Europe lockers are typically inside the classroom and not all students have access to them as their number is limited.
6. Dress Code
High school students in the U.S. are not supposed to wear any school uniform, so they mostly wear whatever they want as long as it looks neat and decent. They can purchase t-shirts, sweatshirts or hoodies with their school logo, but only if they wish. Most high schools in Europe require their students to wear school uniform they have to purchase and wear it at least during special events when they represent the school.
7. Curriculum
The curriculum in the USA and Europe is a little bit different. Among the facts that surprise me most is that students in America don't have an extended list of subjects that is the same for the whole year or several years. For example, in Europe all students study Chemistry for several years in a row and the same is true about biology or physics. And these subjects don't change, students keep learning them for 4 years until graduation. In the U.S. students may have a particular set of subjects in the fall term and a different set of subjects in the spring term. For example, Geography is among the electives in high school, and they have particular subjects as intensive courses which are followed by other courses the next term.
After studying in Ukraine, which has European model of education, my son said he loved American system of education more. It allows more freedom and flexibility, takes into account the student's talents and aspirations, and offers more free time to be engaged in hobbies and sports.