The punctuation rules to memorize for ACT English are commas, semicolons, colons, dashes, and apostrophes, plus the clause logic behind each. Punctuation is one of the most tested parts of the section, and it's also one of the most learnable.
Commas
Use commas after introductory phrases, around non-essential information, and before a coordinating conjunction joining two independent clauses. Don't use a comma to join two complete sentences alone; that's a comma splice, and it's one of the ACT's favorite traps.
Semicolons
A semicolon joins two independent clauses (each could stand alone). If you can replace it with a period, it's correct. This makes semicolon and period answers functionally interchangeable on the ACT; if both are options without other differences, neither is the answer.
Colons
A colon introduces a list, explanation, or example and must follow a complete sentence. "She packed three things: a map, water, and a snack" works; placing a colon mid-clause does not.
Dashes
Dashes work like commas (for non-essential info) or like a colon (to introduce). A pair of dashes must match; don't open with a dash and close with a comma.
Apostrophes
Apostrophes show possession (the student's book, the students' books) or contraction (it's = it is). The classic trap: its (possessive) vs it's (it is), and their/there/they're. These show up often in common question types.
Practice clause spotting
Most punctuation questions come down to one skill: deciding whether each side of the mark is an independent clause. Drill that on thirty-six's concept quizzes, and fold it into the full rule set in the grammar rules tested on the ACT.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
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