Common Song Structure

Intro

Verse: Usually two to three verses in a song with similar melody but a change in lyrics

Chorus: A chorus is a repeated section of  a song after each verse. This section of lyrics repeated within a song, is typically the most rememberable and often times has the same words repeated multiple times within the chorus. After the first verse comes the hook, which is the most memorable (and often most important) part of many hip-hop songs.

Hook: A portion of lyrics or beat structure that is repeated and catches ones attention, or hooks the listener. The hook often gets stuck in your head. The hook can be part of a chorus. A repetead musical idea, phrase or riff.

It's important to have the hook accomplish two things. First, it must be fun to listen to, because it's the part that listeners are going to hear the most. This, I'm sure, is what The Sugarhill Gang was thinking about with this hook on "Rapper's Delight":

I said a hip-hop, the hippie the hippie,
To the hip hip-hop, uh you don't stop the rockin',
To the bang bang, say up jumped the boogie, 
To rhythm of the boogie the beat.

That hook doesn't make any sense, but it is fun and oddly catchy. The second thing most hooks should do is advance the main idea of the song. Often, the best hooks do this without being obvious. Take this example from Jay-Z on a track where he basically just brags:

Can't touch the untouchable, break the unbreakable
Shake the unshakeable (it's Hovi baby) 
Can't see the unseeable, reach the unreachable,
Do the impossible (it's Hovi baby)

He doesn't use the hook to come out and just say, "I am awesome," but that is the message. Since your students are writing an academic song, they'll want to think of a hook that can complement the subject. Students should always come back to the hook once they've written the whole song to see if they can improve it. Hooks are extremely important.

Bridge: Typically after the second chorus, the bridge though similar to the rest of the song has a change in melody, lyrics and background music from the rest of the song.