高校生です

is a high school student

→ 高校生
phrase Uncommon #11,365
is a high school student です is the polite form of “to be.” The subject is understood from context.
JA: 妹は高校生です。
EN: My younger sister is a high school student.

トムも私も高校生です。

Both Tom and I are high school students.

トムはごく普通の高校生です。

Tom is an ordinary high school student.

私たちは高校生です。

We are high school students.

私はまだ高校生です。

I'm still a high school student.

私の弟は高校生です。

My younger brother is a high school student.

彼は高校生です。

He is a high school student.

私は高校生です。

I am a high school student.

高校生ですか?

Are you a high school student?

彼らは高校生です。

They are high school students.

彼も私も高校生です。

He and I are both high school students.

トムは高校生です。

Tom is a high school student.