Today was the fourth day of 6th grade.
> Today is my fourth day in 6th grade.

I got up at 6:20, and I did Kumon(It's like a home - school material.).
> I got up at 6:20 and did Kumon (it's like a home - school material). or
> I got up at 6:20 and did Kumon. It's like a home - school material.

I ate breakfast, too. It was good.
> Correct!

Then I prepared to go to school.And I went to school.
> Then I prepared to go to school and left after I finished.

I was not late but also not early.
> I?arrived on time.

I read a book before the class begins.
> I read a book before the class began.

The book's title is 'Black Fox'. It was interesting.

> Correct!

Then we had election for our class.
> Then we had the election for the officers of the class.

Then we painted 'smiling faces'.
> Correct!

And we studied science and social studies.
> We also studied science and social studies.

We had lunch. Then we studied English(It was easy.).
> We had lunch. Then we studied English(it was easy). or
> We had lunch. Then we studied English. It was easy.

And went back home.
> Then I went back home.