The SAT’s Reading & Writing section tests grammar in a very specific way. It isn’t asking you to recite rules or label parts of speech — it’s presenting you with a sentence that has one thing wrong and asking you to fix it. That sounds simple, but the test is carefully engineered to make incorrect answers feel natural and correct answers feel awkward. Understanding why a rule exists, not just what it says, is what separates students who consistently get these right from students who keep second-guessing themselves.

After more than 20 years of SAT tutoring and several editions of Barron’s SAT prep books, I’ve seen the same grammar patterns tested over and over. This post walks through the categories that matter most and the specific traps the SAT sets within each one.

Study the rules interactively: I’ve put together a free reference covering all 37 essential SAT grammar rules, organized by category. Each rule includes an explanation, a correct example, an incorrect example, and a targeted SAT tip.

Open the SAT Grammar Rules Reference →

Punctuation: The Most Tested Category

Punctuation questions — commas, semicolons, colons, dashes, and apostrophes — make up a large share of the grammar questions on the digital SAT. The good news is that punctuation follows strict, learnable rules. The bad news is that most students learned these rules loosely and have a lot of “sounds right” habits to unlearn.

Commas are the single most tested punctuation mark. The SAT tests nine distinct comma rules, including when to use a comma with a coordinating conjunction (only when joining two independent clauses), when to set off non-essential clauses, and when commas are flat-out wrong. The trap the test sets most often is placing a comma before “and” when the second half of the sentence isn’t a complete clause — “She studied hard, and passed the exam” is wrong because “passed the exam” has no subject of its own.

Semicolons are simpler than most students think. A semicolon can only connect two independent clauses — two parts that could each stand alone as complete sentences. If you replace the semicolon with a period and both halves still work, the semicolon is correct. If one half is a phrase or dependent clause, the semicolon is wrong. That’s the entire rule.

Colons follow an equally clean rule: whatever comes before the colon must be a complete sentence. Students frequently write things like “My goals are: to finish early and sleep well” — but “My goals are” is not a complete sentence, so the colon is wrong. Cover everything before the colon and ask whether it can stand alone. If not, remove the colon or restructure.

Dashes trip students up because they look like commas but work differently. When two dashes interrupt mid-sentence, they must work as a matched pair — whatever opens the interruption with a dash must close it with a dash. You can’t open with a dash and close with a comma. A single dash at the end of a clause introduces an elaboration or surprise, functioning similarly to a colon.

Apostrophes come down to three things: singular possession (add ‘s, always, even for words ending in s), plural possession (add just an apostrophe after the s for regular plurals), and the its/it’s distinction — one of the most frequently tested traps on the entire test. “It’s” always means “it is” or “it has.” “Its” is possessive and never takes an apostrophe. Substitute “it is” whenever you see “it’s” — if the sentence falls apart, drop the apostrophe.

Verb Agreement: Harder Than It Looks

Subject-verb agreement seems basic until the SAT starts hiding the subject. The test’s favorite technique is to insert a long prepositional phrase between the subject and verb so that students match the verb to the wrong noun. “The list of requirements are long” sounds fine because “requirements” is right next to “are” — but the subject is “list,” which is singular, so the correct verb is “is.” The fix: mentally cross out everything between the subject and verb and check the agreement in isolation.

The test also exploits inverted sentences that start with “there” or “here.” In “There is three main reasons for the delay,” the subject isn’t “there” — it’s “reasons,” which is plural. Flip the sentence: “Three main reasons are there.” Now the agreement is obvious.

Collective nouns are another reliable trap. On the SAT, words like team, committee, group, and jury are always treated as singular in American English. “The committee have reached their decision” is wrong; “the committee has reached its decision” is correct.

Pronouns: Two Separate Issues

Pronoun questions on the SAT involve either agreement or case. Agreement means the pronoun must match its antecedent in number. The trap is that the SAT often uses “their” with a singular antecedent, which has become acceptable in everyday speech but remains incorrect on the test. “Every student must submit their own work” sounds natural, but the SAT expects number consistency throughout.

Case means using the right pronoun form depending on its role in the sentence. Object pronouns (me, him, her, us, them) must be used after prepositions. “Between you and I” is one of the most common errors in English — and the SAT tests it regularly. Remove the other person: you’d never say “between I.” The preposition requires an object pronoun, so “between you and me” is correct.

Pronoun shift — moving from “one” or “a person” to “you” within a sentence — is also tested frequently. A sentence that begins “When one works hard” must stay in third person: “one tends to succeed,” not “you tend to succeed.”

Modifier Placement: Logic Over Grammar

Modifier questions test whether a descriptive phrase is logically connected to the right noun. An introductory participial phrase must modify the grammatical subject of the main clause — the first noun after the comma. “Running through the park, a deer was spotted” is wrong because the deer isn’t doing the running. The correct version establishes a logical subject: “Running through the park, she spotted a deer.”

The that/which distinction is closely related and tested frequently. “That” introduces essential (restrictive) clauses — information needed to identify which noun you mean. “Which” introduces non-essential clauses — extra information set off by commas. “The book that won the award” limits which book. “The book, which won the award,” adds information about a book already identified. If you can remove the clause without losing the sentence’s core meaning, use “which” with commas.

Transitions: Matching the Logic Between Ideas

Transition questions ask you to pick the word that correctly signals the logical relationship between two ideas. The test gives you four options — typically a contrast word, an addition word, a cause-and-effect word, and an illustration word — and you need to read both clauses carefully to determine which relationship is actually present.

The most common trap is choosing a word that sounds sophisticated rather than one that fits. Students reach for “however” when the sentence actually calls for “furthermore,” or use “consequently” when the second clause is an example rather than a result. Read the two ideas, decide whether they agree or disagree, whether one causes the other, or whether the second illustrates the first — then match the transition word to that relationship.

Verb Tense: Consistency and Sequence

Tense questions come in two forms. The first is simple consistency: if a passage is written in the past tense, a verb that randomly shifts to present tense is wrong. Always scan the surrounding sentences for tense context before choosing — the underlined portion doesn’t exist in isolation.

The second form involves sequence of events. Use the past perfect (had + past participle) to show that one past action was completed before another. Signal words like “by the time,” “before,” and “after” are the SAT’s way of telling you that sequencing matters in that sentence. “By the time she arrived, the meeting ended” should be “the meeting had ended” — it was done before she got there.

Conditionals are tested too. Real or possible conditions use present + future: “If she studies, she will pass.” Hypothetical conditions use past + would: “If she studied, she would pass.” The trap the SAT sets almost every time: “would” in the if-clause. Never write “If she would study” — “would” belongs in the result clause, not the condition.

Where to Go From Here

The seven categories above — commas, other punctuation, verb agreement, pronouns, modifier placement, verb tense, and transitions — cover the vast majority of grammar questions on the digital SAT. Mastering them isn’t about memorizing rules in the abstract; it’s about recognizing the specific traps the test sets within each category and building reliable habits for catching them.

Once you’ve reviewed the rules, put them to work in context with our SAT Reading & Writing practice drills — 40 drills covering every question type, each with five questions and full explanations. And if you want to build the vocabulary that helps with the harder Reading & Writing questions, the SAT Vocabulary Flashcards are a good complement to grammar work. For math prep alongside your Reading & Writing study, see the SAT Math drills.

Free SAT Grammar Rules Reference — all 37 rules across 7 categories, with explanations, correct and incorrect examples, and targeted SAT tips for each one. Browse the full list or expand individual sections as you study.

Open the SAT Grammar Rules Reference →