Please can somebody ELI5 the English secondary school system

[MerlotMisery]

Scot living in England here.

The English secondary school system confuses me immensely.

First of all, we call Reception to Year 6, Primary 1 to Primary 7. Then Secondary school years are called S1 to S6 (I believe in England this would be Year 7 to 12, with 12 also known as 6th form, is this right??)

Secondly, when I was at school there were exams called Standard Grades which I understood to be vaguely equivalent to GCSEs, and Highers which I understood to be vaguely equivalent to A-levels. Universities would list entry requirements in terms of Higher exam results.

In Scotland your secondary school career looked like this:

S1 and S2: mess about fairly aimlessly. Work out which subjects you like or are good at. At the end of S2, pick 8 subjects for Standard Grade.

S3 and S4, study subjects with exams at the end of S4. So Standard Grades were 2-year courses. Then pick up to five subjects for Higher. You could substitute some of these for other modular courses if you wanted.

S5 study your Highers and modules, exams at the end of S5. So Highers are 1-year courses.

S6, pick some other Highers, or repeat any you failed in S5. Or do an even higher qualification called a certificate of sixth year studies.

Please could somebody with knowledge of a standard English secondary school career explain the equivalent?

Thanks.

Year 7-9 is key stage 3, broad curriculum similar to S1 and S2, then 10-11 is key stage 4 and level 2 qualifications mostly GCSE'S, where children generally study English, Maths, science, a language, a humanity and a couple of choices (varies by school and aptitude of the child). Can then leave school after year 11 and go to college, get a job, apprenticeship or stay in a school setting for Year 12 and 13, 3 or 4 subjects at A level (more academic) or BTEC level 3 or T levels (more practical/ skills based). Highers are due to being 1 year and about half the content of an A level, hence the difference when you look at entry between Scottish and English entry requirements.