I wanted to give you a brief explanation, but I ended up summarising the entire
Dutch school system. I also just found out there's a comprehensive-looking
Wikipedia article [10] on the matter, so perhaps this wall of text is
unnecessary. I have added sources, primarily on Wikipedia, some in Dutch and
some in English. I only used them to check some facts.

How the Dutch school system works:

The school system in the Netherlands is separated into three stages: primary
school, secondary school, and higher education.

Primary school is separated into 8 stages, which normally correspond to years.
These are "group 1" to "group 8". Children start school roughly when they are 4
years old, but education is compulsory from age 5. These 8 years increasingly
introduce different subjects and increase difficulty, with reading, spelling,
and arithmetic in group 3, English starting in group 7, etc [1].

During primary school, progress of each student is tracked using tests,
allowing the teacher to see how the child develops. Near the end of primary
school, the teacher gives a formal "school advice" for the secondary school
level. There's also a final test after this, and if the student excels
unexpectedly the school needs to reconsider their advice and possibly adjust
it. This test is an extra piece of data for the secondary school to consider.

The primary school's advice determines which level of secondary schooling the
student can enter [2]. The secondary school may not base their acceptance on
other tests and may not require any extra tests, unless they provide a
"special" kind of education, like bilingual education or education focused at
professional sports. In that case, the extra test may only test the student's
special abilities required for the school.

Secondary school [3] generally takes between 4 and 6 years, and is divided into
four levels of increasing difficulty: practical education, vmbo (+ mbo),
havo, and vwo. Practical education [4] does not have a specified duration
and is meant for students with particularly low intelligence (60 to 75-80) and
a learning delay of at least 3 years. Vmbo [5] is preparational secondary
vocational education and is again divided into 4 levels, in increasing order
of theory-orientedness. It takes 4 years and ends with a final, nationwide
exam. It prepares the student for a job, for havo or for mbo. About 60% of
all students in secondary education follow vmbo.

After vmbo the student can go to mbo [6], which is secondary vocational
education. It is focused at joining the job market and, again, divided into 4
levels. The first level does not actually require any previous qualifications
and educates the student to become an assistant professional, the second
level prepares the student to become a basic professional, the third level
prepares the student to become an independent professional, and the fourth
level prepares the student to become a specialized professional. The fourth
level also allows the student to progress to hbo. Mbo corresponds roughly to
community college in the US.

Havo [7] is higher general secondary education, takes 5 years, and is
followed by about 20% of all secondary education students. Havo prepares the
student for hbo, but after 3 years one can also be admitted to mbo. Vwo [8]
is preparational scientific education, takes 6 years, and is also followed by
about 20% of all secondary education students. It comes in a few variants,
primarily atheneum and gymnasium. The difference between those is that
gymnasium includes Latin and/or Greek. Vwo prepares the student for wo.

Higher education consists of hbo [9], higher vocational education, and
wo, scientific education. Hbo is focused at the application of scientific
knowledge, while wo is focused at scientific research. These follow the
international standards for higher education.

As an aside, the terminology around higher education can be a bit confusing
when translating between Dutch and English. Hbo is delivered at a "hoge
school", which translates literally to English as "high school". The proper
English term is "university of applied sciences". Furthermore, in Dutch wo is
commonly (even usually) called "universiteit", Dutch for "university". When
doing hbo, saying in English that you are a university student may therefore
feel like a lie, while being correct.

[1] (Dutch): https://nl.wikipedia.org/wiki/Basisonderwijs_in_Nederland

[2] (Dutch): https://www.rijksoverheid.nl/onderwerpen/toelating-middelbar...

[3] (Dutch): https://nl.wikipedia.org/wiki/Voortgezet_onderwijs

[4] (Dutch): https://nl.wikipedia.org/wiki/Praktijkonderwijs

[5] (English): https://en.wikipedia.org/wiki/Voorbereidend_middelbaar_beroe...

[6] (Dutch): https://nl.wikipedia.org/wiki/Middelbaar_beroepsonderwijs

[7] (English): https://en.wikipedia.org/wiki/Hoger_algemeen_voortgezet_onde...

[8] (English): https://en.wikipedia.org/wiki/Voorbereidend_wetenschappelijk...

[9] (Dutch): https://nl.wikipedia.org/wiki/Hoger_beroepsonderwijs

[10] (English): https://en.wikipedia.org/wiki/Education_in_the_Netherlands