Opeth for homework?

I think I would go with a song from SL or BWP. I was thinking of either Drapery or White cluster. Both songs are pretty accessible and have meaningful lyrics as well.
 
I would take, then, Credence for two reasons:

1) you won't hurt people's ears in the class (this'd happen if you play Serenity).

2) credence is shorter, really melancholic, you can refer to the whole concept of the MAYH album, and it's kind of more accessible (more people will like it, and you won't feel as angry. What I mean is it happened to me that I played a song I really liked in front of the class, and the people there didn't give a shit about it: this is, believe you me, a horrible feeling)
 
i love opeth's lyrics of course but if you really wanna impress everyone, how about king crimson's "epitaph":

the wall on which the prophets wrote
is cracking at the seams.
upon the instruments of death
the sunlight brightly gleams.
when every man is torn apart
with nightmares and with dreams,
will no one lay the laurel wreath
when silence drowns the screams.

between the iron gates of fate,
the seeds of time were sown,
and watered by the deeds of those
who know and who are known;
knowledge is a deadly friend
if no one sets the rules.
the fate of all mankind i see
is in the hands of fools.

confusion will be my epitaph.
as i crawl a cracked and broken path
if we make it we can all sit back
and laugh.
but i fear tomorrow i'll be crying,
yes i fear tomorrow i'll be crying
 
Although a lot of Tool's lyrics are quite.. "pseudo-intellectual", they do a good job for a detailed analysis. You should check google for "46&2" for example. I dont like the song too much, but i found a lot of material as i did research for a project for my religion class. I ended up with about 20 pages and the best grade possible.
 
Take in Demon Of The Fall...it is brutal and it has the melodic section at the end. Then you get to explain the story behind MAYH, and you get to play an awesome song that will undoubtedly scare the class. Open their ears to something that isn't watered-down commercial bullshit.