The Complete Guide to SAT Sentence Structure Questions: How to Spot and Fix Errors That Trip Up Most Students

TLDR:

• Run-on sentences appear in roughly 30% of SAT Writing questions and need proper punctuation or conjunctions.
• Sentence fragments lack either a subject or complete verb and are easier to spot when you read them aloud.
• Parallelism errors occur when items in a list or comparison don't match grammatically.
• The SAT tests the same 3-4 sentence structure patterns repeatedly once you know them.

Here's what no one tells you about SAT sentence structure questions: they're not testing whether you know grammar terminology. The College Board doesn't care if you can define a subordinating conjunction. They want to see if you can recognize when a sentence doesn't work—and more importantly, fix it.

After working with hundreds of students on SAT prep, I've noticed something consistent. Students who struggle with sentence structure questions aren't necessarily weak writers. They've just never been taught to listen for structural problems. Let's change that.

Run-On Sentences Are the Most Common SAT Sentence Error (And the Easiest to Fix)

A run-on sentence happens when two complete thoughts crash into each other without proper punctuation or connection. The SAT loves testing these because students often don't hear them as errors—especially if the sentence "sounds" okay.

Here's a classic example:

Incorrect: The scientist presented her findings at the conference, her research challenged existing theories about climate patterns.

Both parts could stand alone as sentences:

• "The scientist presented her findings at the conference."
• "Her research challenged existing theories about climate patterns."

That comma isn't strong enough to hold them together. You have four solid fixes:

1. Use a period: The scientist presented her findings at the conference. Her research challenged existing theories about climate patterns.

2. Use a semicolon: The scientist presented her findings at the conference; her research challenged existing theories about climate patterns.

3. Add a coordinating conjunction: The scientist presented her findings at the conference, and her research challenged existing theories about climate patterns.

4. Make one part dependent: The scientist presented her findings at the conference, where her research challenged existing theories about climate patterns.

The SAT typically gives you answer choices that test whether you know these options. Here's the pattern you'll see repeatedly: one choice will be the run-on (wrong), one will use just a comma (still wrong—that's called a comma splice), one will have a semicolon or period (often right), and one will add a conjunction.

Warning: Don't assume the shortest answer is correct. The SAT knows students gravitate toward brevity, so they'll often make the grammatically correct answer slightly longer.

Comma Splices Are the Variation That Fools Everyone

The comma splice deserves special attention because it's the run-on error that appears most frequently on actual tests. It's when two independent clauses are joined with only a comma—no conjunction, no semicolon, nothing else.

Incorrect: The museum reopened after renovations, visitors lined up for hours to see the new exhibits.

Students miss these constantly because we use comma splices in casual writing all the time. Text messages, social media posts, even published articles sometimes bend this rule. But the SAT doesn't bend.

Here's what makes comma splices especially tricky: they often appear in sentences where the two parts are closely related in meaning, making them feel correct.

The team practiced every day, they were determined to win the championship.

Feels okay, right? It's still wrong. You need a semicolon, a period, or a conjunction after "day." The closeness of the ideas doesn't matter—the grammar still requires proper punctuation.

I had a student last year who scored 650 on her first SAT Writing section. We reviewed her mistakes, and 11 out of 13 errors were comma splices she didn't recognize. After two focused practice sessions where she learned to spot independent clauses, she jumped to 710. That's how much this one pattern matters.

Sentence Fragments Are Incomplete Thoughts Masquerading as Sentences

A fragment is missing something essential—usually a complete verb or an independent clause. The SAT disguises fragments by making them long or by placing them near complete sentences.

Incorrect: Although the director had won numerous awards for her previous films and was considered one of the most innovative voices in modern cinema.

This is a fragment because "although" makes the entire thing dependent. It's waiting for a main clause that never arrives. You're left hanging, thinking, "Although all that... what?"

The fix is straightforward—remove "although" or add an independent clause:

Correct: Although the director had won numerous awards for her previous films and was considered one of the most innovative voices in modern cinema, her latest work received mixed reviews.

Here's the pattern that catches students: fragments often start with subordinating words like:

• Although
• Because
• Since
• While
• When
• If
• Unless

If you see these words at the beginning of an underlined portion on the SAT, immediately check whether there's a complete independent clause somewhere. If not, you've found your error.

Another common fragment type is the "-ing" fragment:

Incorrect: The author researching 17th-century manuscripts in libraries across Europe.

"Researching" isn't a complete verb. It needs a helping verb ("was researching") or you need to change it ("The author researched").

Here's the trick I teach: cover up everything before the first comma in a sentence. Can what remains stand alone? Now cover up everything after the comma. Can that stand alone? If you have two independent clauses with just a comma, that's a run-on. If you have a dependent clause with no independent clause, that's a fragment.

One of my students calls this the "cover-up test," and she used it to catch 8 out of 9 sentence structure errors on her last practice test.

Parallelism Errors Happen When List Items Don't Match

Parallelism means keeping grammatical structures consistent within a sentence. When you list items, compare things, or show a series of actions, they all need to match grammatically.

The SAT tests this relentlessly.

Incorrect: The job requires attention to detail, working well under pressure, and to communicate effectively with clients.

See the problem? We have:

• attention (noun)
• working (gerund)
• to communicate (infinitive)

Pick one structure and stick with it:

Correct: The job requires attention to detail, ability to work well under pressure, and effective communication with clients.