YOU SAID:

I think he knows that she was going to be at school today because he had been there.

INTO JAPANESE

彼はそこにいたので、彼女が今日学校に行くことを知っていたと思います。

BACK INTO ENGLISH

I think he knew she was going to school today because he was there.

INTO JAPANESE

彼はそこにいたので、彼女が今日学校に行くことを知っていたと思います。

BACK INTO ENGLISH

I think he knew she was going to school today because he was there.