Fyi: it’s called post secondary because, I think, UK calls it primary, secondary, and after that is post secondary.
US.
Middle School and Jr. High vary depending on how the grades break.
When I was coming up it was this:
Grade School: 1-6
Jr. High - 7-9
High School - 10-12
But when I hit 9th grade, they changed it:
Grade School: 1-5
Middle School: 6-8
High School: 9-12
Slovakia.
If I am to translate it word-to-word:
Základná škola - Base school (so primary) (9 years) - split into 1st degree (1-4) and 2nd degree (5-9).
Stredná škola - Middle school (2-5 years based on field of study, 4 and 5 year fields are with graduation)
Get ready for a twist: Gymnasium (8 or 4 years) - 8 year gymnasium starts after 5th grade of primary school and 4 year after 9th grade. They also replace middle school. It’s not that popular since you basically won’t get any job without college with gymnasium. It’s really just a preparation for college (literally “high school” (Vysoká škola)) (though perhaps better than middle school).
US. In my dialect, all three are different.
Middle school: 6-8
Intermediate school: 7-8
Jr High: 7-9
I attended an intermediate school that called itself a jr high, so I can understand the confusion.
For my state in Australia its
Kinder Ages 3-5
Prep Ages 5-6
Primary School Ages 6-12, called Grade 1-6
Secondary/High School Ages 12-18, Called Years 7-12
After that you’ve got higher education choices via TAFE or University, theres no cut off ages for that.
School is mandatory from ages 6 To 17.
Finland
0-5 year olds Kindergarten (voluntary)
6 y.o.'s pre-school (mandatory since 2018)
Grades 1-6 in comprehensive school are called “low school” (mandatory) Grades 7-9 in comprehensive school are called “high school” (mandatory)
Second degree years 1-3 (mandatory since 2021), you choose either “upper secondary (gymnasium)” or vocational school (or both).
And if you wish to study further university/uni of applied sciences. Basically everyone does their masters (3+2 years) if they choose uni. Uni of applied sciences is usually 3 years.