5 ACT English Grammar Rules Students Miss Most

Many students lose more points on ACT English than they expect, not because they are bad writers, but because the ACT tests a narrow, predictable set of grammar and punctuation rules. School English classes often emphasize essays, literature, and broad communication skills. The ACT English section is different. It asks students to make fast, rule-based editing decisions under time pressure.

The good news is that the most common ACT English grammar rules can be learned. Once students know what the test is asking, they can stop relying on what “sounds right” and start using a repeatable process. Below are five ACT English rules Northside Tutoring sees students miss again and again, along with sample questions and practical ways to avoid those mistakes on test day.

1. Subject-Verb Agreement with Intervening Phrases

Subject-verb agreement sounds simple: singular subjects take singular verbs, and plural subjects take plural verbs. The ACT makes this harder by placing extra words between the subject and the verb. Those extra words often distract students into matching the verb to the nearest noun instead of the real subject.

ACT-style trap:

The results of the science experiment shows a clear pattern.

The noun closest to the verb is experiment, which is singular. But the subject of the sentence is results, which is plural. The phrase of the science experiment is only describing the results. It does not control the verb.

Corrected sentence:

The results of the science experiment show a clear pattern.

On the ACT, students should pause whenever a verb is underlined and ask, “What is the subject of this verb?” Then they should mentally cross out interrupting phrases such as of the study, with several examples, including the final chapter, or as well as the other students. The verb must agree with the true subject, not with any noun inside those extra phrases.

2. Comma Splices Between Complete Sentences

A comma splice happens when two complete sentences are joined with only a comma. This is one of the most common punctuation errors on ACT English because the sentence often feels smooth when read quickly.

ACT-style trap:

The ACT begins early in the morning, students should arrive before the doors open.

Both sides of the comma can stand alone as complete sentences:

• The ACT begins early in the morning.
• Students should arrive before the doors open.

A comma alone cannot join those two independent clauses. Students have several correct options:

• Use a period: The ACT begins early in the morning. Students should arrive before the doors open.
• Use a semicolon: The ACT begins early in the morning; students should arrive before the doors open.
• Use a comma plus FANBOYS conjunction: The ACT begins early in the morning, so students should arrive before the doors open.
• Use a subordinating conjunction: Because the ACT begins early in the morning, students should arrive before the doors open.

The fastest ACT check is to read both sides of a comma. If each side could be its own sentence, a comma by itself is wrong.

3. Apostrophes: Possession, Contractions, and Plurals

Apostrophe questions are small, but they cost students easy points. The ACT often tests whether students know the difference between a contraction, a possessive, and a plural noun.

The most common example is its versus it’s:

• It’s means it is or it has.
• Its means belonging to it.
• Its’ is not correct.

Worked example:

The school improved [its / it’s] average ACT score by four points.

Test the contraction by substituting it is:

The school improved it is average ACT score by four points.

That does not make sense, so the correct answer is its.

The same process works for other commonly confused words. They’re means they are, their shows possession, and there refers to a place or introduces a sentence. You’re means you are, while your shows possession. On test day, students should slow down on apostrophe questions. These are usually rule checks, not style questions.

4. Run-On Sentences and the FANBOYS Test

A run-on sentence is not just a long sentence. A long sentence can be perfectly correct if its clauses are joined properly. A run-on occurs when two complete thoughts are fused together without proper punctuation or a proper connector.

ACT-style trap:

Maya studied for six weeks she improved her ACT English score by six points.

This sentence contains two complete thoughts:

• Maya studied for six weeks.
• She improved her ACT English score by six points.

They need a valid connector.

Corrected with a semicolon:

Maya studied for six weeks; she improved her ACT English score by six points.

Corrected with a FANBOYS conjunction:

Maya studied for six weeks, and she improved her ACT English score by six points.

FANBOYS stands for for, and, nor, but, or, yet, so. These are coordinating conjunctions. When a FANBOYS word joins two independent clauses, a comma comes before it. When it joins only words or phrases, no comma is needed.

Comma needed: She studied hard, but the passage was still difficult.

No comma needed: She studied hard but remained nervous.

The difference is that the passage was still difficult is a complete sentence, while remained nervous is not.

5. Misplaced and Dangling Modifiers

Modifiers describe other words in a sentence. The ACT tests whether the modifier is placed next to the word it logically describes. If the modifier is too far away, or if the word being described is missing, the sentence becomes confusing or unintentionally funny.

Dangling modifier:

Having studied all weekend, the practice test felt manageable.

The opening phrase says someone studied all weekend. But the noun after the comma is practice test. A test cannot study. The person who studied must appear right after the comma.

Corrected sentence:

Having studied all weekend, Elena felt the practice test was manageable.

Misplaced modifier:

The tutor reviewed the grammar rule with the student that appeared on the ACT.

This sentence makes it sound as if the student appeared on the ACT. The intended meaning is that the grammar rule appeared on the ACT.

Corrected sentence:

The tutor reviewed the grammar rule that appeared on the ACT with the student.

The ACT shortcut is simple: when a sentence begins with an introductory phrase ending in a comma, the subject immediately after the comma must be the person or thing doing the action in that phrase.

How Students Should Practice ACT English Grammar

Knowing these rules is only the first step. ACT English rewards fast recognition. Students should practice by reviewing missed questions and labeling the rule being tested. Was it subject-verb agreement? A comma splice? A modifier? Once students can name the rule, they can fix the pattern instead of treating every missed question as random.

A strong practice routine includes three steps:

1. Do timed passages so students build pacing.
2. Review every missed question and identify the grammar rule.
3. Redo similar questions until the correction becomes automatic.

This is where targeted tutoring makes a difference. A tutor can quickly identify which rule families are costing the most points, then build focused drills around those patterns.

Ready to Stop Losing Points on ACT English?

These five ACT English grammar rules account for a large share of the preventable errors students make on practice tests. But recognizing the rule under timed conditions is a skill of its own. Students need repetition, feedback, and a clear strategy for deciding when a sentence is actually wrong.

Northside Tutoring’s ACT tutors in Atlanta help students work through real ACT English passages, diagnose recurring grammar errors, and practice until the rules become automatic. For students who need broader writing and grammar support, Northside also offers English tutoring and comprehensive test prep for the ACT, SAT, SSAT, and other exams.