In order to find a Dutch primary or secondary school, the website of your municipality is probably a good place to start. Unfortunately, these websites are likely to be in Dutch only. Nonetheless, they will provide you with a list of schools in the region. Please find below a list of words that will be useful in your school search.
The 'Guide to Choosing a School 2020' provides a lot of detailed information about the options for primary education in Leiden. Visit the schools you are interested in on an ‘information morning’ (informatie-ochtend). Ask lots of questions, for example how much experience they have in teaching non-Dutch children. See also the extensive 'Checklist Basisschool'.
Visit several schools so you can get a feel for each school – it is a very personal decision. When deciding upon the school for your child, you determine to a large extent how they will learn academically and how they will grow emotionally, physically and socially.