It is so interesting to browse through a book and deep dive into specific topics out of one's own interest. This experience of learning is very much different from learning via subject books where related topics are grouped into subjects.
Book : Maisy goes to Museum
DD1 read about elephants being woolly and huge. And there were more questions.
Did elephants have hair on their skin earlier ?
Were they very huge, like giant?
Oh, humans also had hair earlier?
She googled(with my help) some pictures, texts about ancient humans.
Book: The Human Body
She read about bones and joints in human body.
Many questions, pointing to various bones that can be felt in our body.
Then, she got so involved that, she started drawing and colouring bones couple of days later.
This experience is so different from what happens in school - opening a subject text, reading out, asking questions and MAKE the child do some activity related to what was introduced(no guarantee if it was actually learnt) in the class. And to reinforce what was taught in class, homeworks, projects, assignments are given to the child that are again done in major part by the parent at home.
See the reality?
To self learn is the best way to learn.