In the first days in elementary school, I couldn't write, and I could answer tests. Did I understand language then?

Now I know I write something every day, but when I entered elementary school I couldn't.

A few month later, there were writing classes in my Japanese classes.
The girl next to me did so well that she requested one and after sheets.
I remember she wrote 4 or 5 sheets in the first writing class.

As for me all I could wrote was three letters that stands for "I".
The first term I could only do this way.
As long as I remember, it wasn't spring vacation, the last of the school year, that I succeeded to write something in my own will, although I couldn't remember it was a diary or a reader's review.

From the first of elementary school I did well in tests, especially in math.
But looking back on then carefully, I doubt I really understand language at that time.
Then, how did I do well in tests?
I guess typical tests were, and are fill-the-blank questions, and I could see what should be in the blank regardless of if I really understood language written on these, or I only understood by images or atmospheres, I could only well guess what it should be.