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.
That didn't even make that much sense in English.