There are numerous resources on-line on grammar and sentence-level conventions. The best is Purdue's On-line Writing Lab (OWL), which covers grammar, citation, academic writing, English as a second language, discipline-specific writing, and also has resources for both teachers and students.
SPU's Writing Program also recommends Mary Norris's "Comma Queen" series on Youtube. Norris is the copy editor for The New Yorker, and her two-minute videos cover commas, split infinitives, ellipses, "I" versus "me", and all sorts of punctuation.
And there's also Bedford's top 20 errors in writing.
The Purdue OWL, Norris's videos, and Bedford's list of errors offer one approach to the sentence, one grounded in rules. And, to some extent, they are useful: writers have to know the rules, have to know how to put subject-verb-object together to make a sentence. But there is another part of teaching the sentence, one grounded in language games. In the spirit of play, Dr. Moe has developed a ten-assignment sequence of Sentence Exercises. These exercises work from the assumption that students learn to write sentence by spending time inside sentences, both their own and those of other writers.
The Good and Bad Sentence
Students select two sentences, one good and one bad, from their most recent reading assignment. They are not to judge these sentences based on content; they are to be concerned with structure. Most students will think “good” means “grammatically correct” and “bad” means “grammatically incorrect," or that "good" and "bad" concern subject matter. Students write a paragraph on each sentence, explaining why it is good or bad, and they revise the bad sentence to make it better.
Exercises in Style
Raymond Queneau's book Exercises in Style retells the same story 99 different times in 99 different ways. In the spirit of Queneau, students rewrite the "good" sentence from the previous exercises at least 15 different ways. They then write a paragraph in response to this question, a question pulled from Verlyn Klinkenborg's Several Short Sentences about Writing: "Why is the sentence this way and not another way?"
Students write a paragraph with no sentence longer than 6 words. The paragraph must be at least 250 words. It can be about any topic.
Students are given a series of short, simple sentences (at least a dozen) and asked to combine them into longer sentences. They are to combine them using any means possible (punctuation, conjunctions, words like “although, since, or because” etc.), sentences like the following:
Peter lives in Pittsburgh.
He lives on Kennebec St.
He likes the Pirates.
He has not been to a Penguins game.
Students put their combined sentences on the board and discuss the differences in meaning when the sentences are combined differently.
Break up a long sentence
Give students the following 116-word sentence from Guy Davenport's "On Reading" and ask them to break it into short sentences. Then discuss the merits of the original against our rewrites. What does the long sentence allow you to do? What does the short sentence allow you do to?
To my Aunt Mae––Mary Elizabeth Davenport Morrow (1881-1964), whose diary when I saw it after her death turned out to be a list of places, with dates, she and Uncle Buzzie (Julius Allen Morrow, 1885-1970) had visited over the years, never driving over thirty miles an hour, places like Toccoa Falls, Georgia, and Antreville, South Carolina, as well as random sentences athwart the page, two of which face down indifference, “My father was a horse doctor, but not a common horse doctor” and “Nobody has ever loved me as much as I have loved them”––and a Mrs. Cora Shiflett, a neighbor on East Franklin Street, Anderson, South Carolina, I owe my love of reading.
The Long Sentence
Students read from Writer's Help sections dealing with commas, colons, dashes, and parentheses, and sections dealing with independent and dependent clauses. Students then write a single sentence of at least 100 words which uses a comma, dash, and parenthetical comment as well as at least one dependent clause. Here's an assignment sheet that gives students guidance in how to go about writing a 100-word sentence.
Sentence or Paragraph Imitation
Give students a piece of good writing, such as the following, from Annie Dillard's An American Childhood:
A baseball weighted your hand just so, and fit it. Its red stitches, its good leather and hardness like skin over bone, seemed to call forth a skill both easy and precise. On the catch--the grounder, the fly, the line drive--you could snag a baseball in your mitt, where it stayed, snap, like a mouse locked in its trap, not like some pumpkin of a softball you merely halted, with a terrible sound like a splat. You could curl your fingers around a baseball, and throw it in a straight line. When you hit it with a bat it cracked--and your heart cracked, too, at the sound. It took a grass stain nicely, stayed round, smelled good, and lived lashed in your mitt all winter, hibernating.
Ask them to imitate it as best they can, retaining the grammatical structure but inserting their own content. Imitation exercises are great for getting students to work with language, and it is way to address the relationship between form and content: students will have to think through what sort of content would work well with the sentence or paragraph form they are working with.
Half as Long
Give students a paragraph, perhaps the following, from Kathleen Jamie's "The Hvalsalen," when she describes walking under a blue whale skeleton hanging from the ceiling of a museum:
Of course, the blue whale was largest of all. I decided to walk under its full length, and count my steps. First, I walked under the smooth horizontal arch of the jaw, and its palate, where the baleen had once hung, sheets of age-browned bone. Then came the solid complications of the skull, now under the barrel of the ribcage, the ribs curving down, enclosing and protecting nothing but air. I kept walking, counting. As I passed the basking shark I surreptitiously touched its cold skin, rough as sandpaper. I passed a dolphin, small and lithe, and making for the door. Still the blue whale went on overhead. Above the basking shark hung a huge sunfish, an eerie-looking object hanging from a wire, more like a black moon with an eye. Still I walked on, counting until the spine ended. Fifty-seven paces. Less an animal, more a narrative. The ancient mariner.
Ask students to cut the paragraph roughly in half. Discuss how they decided what to cut and what specific things they did at the sentence level to make it happen. Then ask them to cut it in half again. This will be harder. Again, discuss how they cut it and why they cut it as they did. Compare the doubly-cut revision to the original: What is gained? What is lost? Which is better?
Give students a paragraph (either from one of their peers or from something published) and have them complete the following for revisions. The point of this exercise is to experiment with language.
Choose one sentence from the paragraph and combine it with the material preceding or following. Make the new sentence at least 50 words long.
Find two other sentences that seem related and combine them using a semi-colon, colon, or dashes.
Choose two or three consecutive sentences and revise them into a series of short sentences containing no more than six words each.
Select one sentence and revise it into a long sentence followed by a very short sentence that packs a punch.
Rewriting Published Writers
Give the students a paragraph from the textbook and have them rewrite it by combining sentences, breaking apart sentences, deleting sections, putting it into a different style—whatever they think is interesting. Share the rewrites, and discuss how the passage has changed and (most important) why the author might have decided to write the passage as she did originally. Also ask the students what situation they could find themselves in that could warrant writing as this writer did, or writing as their rewrites do.