I sort of skipped the entire 18th century in my literary education too.

But what the romantics are reacting against, are Enlightenment notions of progress--specifically scientifically-based progress, but also capitalism.

I might set them up against Leibnitz, Newton, and Hobbes rather than necessarily another poetic movement. The romantics were going for an idea of Man in Nature, becoming divine, the individual voice.

Aestehtically, Wordsworth for one was reacting against cluttered, stilted and unnatural language. Which would be kind of silly to accuse Pope of, come to think of it.

Er...you know, Romanticism didn't just spring to life fully formed without antecedents in classically inclined 18th century poets, right?

While I think what you're essentially wanting to contrast the Romantics with can be found in a lot of poetry of the "Augustan" age and style (Pope's as good an exemplar as any, although I like his predecessor, Dryden, myself), poetry and literature in general in the pre-Blake, pre-Romantic 18th century in England encompassed many styles and some of those (the Churchyard Poets inspired by Thomas Gray, for instance) can be seen as clearing a path and forging the way for Romanticism.

Thomas Gray ('Elegy Written in a Country Churchyard' www.thomasgray.org/cgi-bin/display.cgi ), George Crabbe (a poet greatly admired by Byron), William Cowper-all these poets wrote with a great deal of intimate personal feeling and a keen appreciation for nature. I don't believe Wordsworth, Shelley, et al. would have been quite the same kind of poets they were without these predecessors.

I don't think any single poem can exemplify "classicism" and the 18th century because the category and the period both are far more complex than they're often credited as being. Why not expose your class to Gray and Cowper as well as Dryden and Pope? The 'Elegy' is one of the most beautiful and celebrated poems in the English language and Cowper's 'Olney Hymns' are the source of many familiar quotations in English ("God moves in a mysterious way", "Variety's the very spice of life/That gives it all its flavour" and "I am the monarch of all I survey" are all lines by Cowper). Teaching these along with the more formal verse of the Augustan poets should help your students place Romanticism in context, giving them a more realistic and less, uh, "romantic", view of the Romantic poets.

I agree with the suggestions that it'd be easier to compare the Romantics with the clockwork universe (though Newton himself was mad as a hatter) and tidy Augustan gardens and all the efforts to control human nature, including the effort control society by hanging people for almost everything (as compared with modern efforts to put everyone in prison) and how criminals became heroes as "free spirits" against authority. Their parents and grandparents' generation (I just learned that Wollstonecraft and Godwin knew Thomas Paine who knew Franklin who knew Voltaire who.... I hope nobody had the clap) had tried to redeem mankind with sweet Reason and were spending their last years disappointed by the greed, lust and blood thirstiness of the democratic mob. If they try to read Pope for an introductory class they'll spend all their time trying to decipher it and won't get what you're driving at.
I have much younger students this year (9th graders) and slip in some Romantics when we read Poe. They respond best when I start with very concrete anecdotes about the Romantics reacting to social convention: Aurore Dupin/George Sand wearing pants 100 years before Rosie the Riveter (with a nod to Amelia Bloomer in between); Romantics and intensity of feeling (Keats saving Fanny Brawne's letters and his fear she would catch his TB); TB as a (reputed) disease of sensitive, intelligent types (they all know who Doc Holliday was), and lots of gossip about the Shelleys and Byron. (We go into more detail with Poe's life, starting with WHY he thought all poetry started with a Dead Young Girl.)
Damnit, there's no much concrete advice here but I've already spent too much time babbling to delete it.