YOU SAID:

School is quite mediocre.

INTO JAPANESE

学校はかなり平凡です。

BACK INTO ENGLISH

School is pretty mediocre.

INTO JAPANESE

学校はかなり平凡であります。

BACK INTO ENGLISH

School is pretty mediocre in.

INTO JAPANESE

学校はかなり平凡なのです。

BACK INTO ENGLISH

It is pretty mediocre schools.

INTO JAPANESE

かなり平凡な学校です。

BACK INTO ENGLISH

This is a pretty mediocre schools.

INTO JAPANESE

これは、かなり平凡な学校です。

BACK INTO ENGLISH

This is a pretty mediocre schools.