Copyright rules?

If is is being done for "non-profit classroom use" under supervision of a teacher, as a bona fide educational lesson, then performance of a lawful copy of any copyrighted sound recording may be exempt from infringement, at least under US copyright laws.

Similarly, if it is performed in public but the performers are not being paid, the performance is not being transmitted, it is non-dramatic music, and any profit from the audience goes to a charitable purpose, it may also be exempt under US copyright laws. 17 USC § 110(4). Look it up.

We're just guessing that US laws (or similar) might apply, and otherwise you would need to state what country you're in, as part of your question.

In theory, non-exempt use would need a license, including possibly a "royalty-free" or "courtesy" license from the owners of the copyright of any sound recording or copyrighted composition you intend to perform.

If the rights holder to a song wanted to make a fuss, they/he/she could sue for any recognizable use. The law is deliberately non-specific about time or number of lines. Even the lyricist, without the band, could sue.

The odds are excellent they won't, but it's worth clearing up.

I don't know if it's copyright law or your teacher's rule, but yes its true, you can only use 30 seconds of a song.

Technically you can't use any of it.

why would she lie? she's trying to protect you and the school