How to Teach Grammar in Third Grade: Complex Sentences, Commas, Apostrophes, and Parts of Speech

By third grade, your child has been writing sentences for a couple of years. They probably capitalize the first word, end with a period, and can identify a noun and a verb if you ask them directly. But their writing likely sounds choppy — a string of short, simple sentences that all start with "I" or "The." Third grade is when grammar instruction shifts from basic mechanics to genuine craft: combining sentences, using commas and apostrophes correctly, and understanding the parts of speech well enough to make deliberate choices. This is the year grammar stops being a set of rules to memorize and starts becoming a tool for better writing.

What the research says

The Common Core Language standards for third grade (L.3.1 and L.3.2) ask students to form and use simple, compound, and complex sentences, use commas and quotation marks in dialogue, form and use possessives, and demonstrate command of standard English conventions. Research by Graham and Perin (2007) in their meta-analysis Writing Next found that sentence-combining instruction — teaching students to join short sentences into longer, more complex ones — is one of the most effective writing interventions available, producing significant gains in writing quality. The key finding: grammar instruction works best when it is connected to the child's own writing, not taught as isolated worksheet exercises.

What to do: Four skills to teach

Skill 1: From simple to compound sentences (2-3 sessions)

Your child probably writes sentences like: "The dog ran. He was fast. He caught the ball." The first step is teaching them to combine simple sentences using coordinating conjunctions.

Teach the FANBOYS. The seven coordinating conjunctions are: For, And, Nor, But, Or, Yet, So. For third grade, focus on the big three: and, but, and so.

Activity: Sentence Surgery

Write two short sentences on index cards. Have your child "operate" on them by choosing a conjunction to stitch them together.

Parent: "Here are two sentences: 'The cat climbed the tree.' and 'The cat couldn't get down.' Can you combine them into one sentence?"

Child: "The cat climbed the tree and the cat couldn't get down."

Parent: "Good start! But you said 'the cat' twice. Can we fix that?"

Child: "The cat climbed the tree but couldn't get down?"

Parent: "That sounds much better. Why did you pick 'but' instead of 'and'?"

Child: "Because the second part is the opposite of what you'd expect."

Parent: "Exactly. 'But' connects ideas that contrast. 'And' connects ideas that go together. 'So' connects a cause and an effect."

Practice tip: Take a paragraph from your child's own writing and have them find places where two short sentences could be combined. This is far more effective than combining sentences from a workbook because the child sees the immediate improvement in their own work.

Then introduce complex sentences. Once compound sentences feel natural (usually after a week or two), introduce the idea of sentences with a dependent clause using words like because, when, if, although, since, and after.

Parent: "Listen to these two sentences: 'We went inside. It started raining.' Can you combine them using the word 'because'?"

Child: "We went inside because it started raining."

Parent: "Now try it with 'when.'"

Child: "We went inside when it started raining."

Parent: "Both work! But notice how they feel a little different. 'Because' tells us why. 'When' tells us the timing. Different connecting words give different information."

Skill 2: Comma rules that matter (2-3 sessions)

Third graders need three comma rules. Do not try to teach all comma rules at once — these three cover the vast majority of what a third grader writes.

Rule 1: Commas in a list (series comma)

Parent: "Write a sentence listing three things you did today."

Child: "I played soccer ate lunch and read a book."

Parent: "Read that out loud. Does it sound right?"

Child: (reads it) "I played soccer... ate lunch and read a book. It's confusing."

Parent: "That's because we need commas to separate the items. Try: 'I played soccer, ate lunch, and read a book.' The commas tell the reader to pause between each item."

Practice with silly lists to keep it fun: "Name five things you'd bring to the moon." Have your child write the sentence and add commas.

Rule 2: Comma after an introductory word or phrase

Sentences that start with words like First, Next, After lunch, Suddenly, or However need a comma before the main sentence starts.

Parent: "Say this sentence: 'After dinner we played a game.' Now say it with a tiny pause after 'dinner.'"

Child: "After dinner... we played a game."

Parent: "That pause is where the comma goes. 'After dinner, we played a game.' The comma tells the reader: the introduction is over, here comes the main idea."

Rule 3: Comma before a conjunction in a compound sentence

When two complete sentences are joined by and, but, or so, a comma goes before the conjunction.

"The dog barked, and the cat ran away." "I wanted to go outside, but it was raining."

Activity: Comma Detective

Print or write a paragraph with all commas removed. Have your child read it aloud and add commas wherever they naturally pause. Then check together against the three rules. This builds the connection between how language sounds and how punctuation works.

Skill 3: Apostrophes — contractions and possessives (2-3 sessions)

Third graders commonly confuse these two uses of apostrophes, and the its/it's distinction will haunt them for years if not addressed now.

Start with contractions because your child already uses them in speech.

Parent: "When you say 'don't,' you're actually mashing two words together. What two words?"

Child: "Do... not?"

Parent: "Right! The apostrophe shows where the missing letters used to be. 'Do not' becomes 'don't' — the apostrophe replaces the 'o' in 'not.'"

Activity: Contraction Match-Up

Write pairs on index cards: "do not / don't," "I am / I'm," "they are / they're," "cannot / can't," "we will / we'll." Shuffle and have your child match them. Then ask them to circle where the missing letters are in each contraction.

Then teach possessives.

Parent: "If the book belongs to Sarah, we say it's 'Sarah's book.' The apostrophe-s shows ownership. Whose book? Sarah's."

Child: "So the apostrophe means something is missing AND it means something belongs to someone?"

Parent: "Exactly — and that's what makes apostrophes tricky. But here's how to tell the difference: if you can expand it to two words (like 'don't' into 'do not'), it's a contraction. If it shows who owns something (Sarah's book = the book of Sarah), it's a possessive."

The its/it's rule: Teach this explicitly and early.

Parent: "'It's' with an apostrophe ALWAYS means 'it is' or 'it has.' You can test it: 'It's raining' = 'It is raining.' Works! But 'The dog wagged it's tail'? Does 'it is tail' make sense?"

Child: "No, that's weird."

Parent: "Right. So the possessive form — meaning the tail belongs to it — has NO apostrophe. 'Its tail.' This is the one weird exception, and even adults get it wrong."

Skill 4: Parts of speech in action (ongoing)

Third graders should be able to identify nouns, verbs, adjectives, and adverbs — not as a vocabulary test, but as a tool for improving their writing.

Activity: Sentence Upgrade

Start with a boring sentence and upgrade it by adding or swapping parts of speech.

Parent: "Here's a sentence: 'The dog ran.' That's a noun and a verb. Pretty basic. Let's upgrade it. What kind of dog?"

Child: "A big, fluffy dog."

Parent: "Those are adjectives — they describe the noun. Now, how did the dog run?"

Child: "Fast?"

Parent: "That's an adverb — it describes the verb. So now we have: 'The big, fluffy dog ran fast.' Way more interesting! Where did the dog run?"

Child: "Across the yard."

Parent: "'The big, fluffy dog ran fast across the yard.' You just built a detailed sentence by thinking about parts of speech."

Activity: Color-Coding

Have your child write 3-4 sentences from their own work. Then use colored pencils: underline nouns in blue, verbs in red, adjectives in green, adverbs in orange. This makes the abstract categories visible and helps children see patterns in their writing (e.g., "I have lots of nouns and verbs but almost no adjectives").

Common mistake: Teaching parts of speech as definitions to memorize ("A noun is a person, place, or thing") without connecting them to actual writing. Your child should be able to use this knowledge, not just recite it. Always follow identification with application: "Now that you see you used the same verb three times, can you replace one with a more specific word?"

How to tell if your child gets it

Your third grader has solid grammar skills when they can:

• Combine two simple sentences into a compound sentence using and, but, or so
• Write a complex sentence using because, when, or if
• Correctly place commas in lists, after introductory words, and before conjunctions
• Use apostrophes correctly in contractions and possessives
• Distinguish between its and it's most of the time
• Identify nouns, verbs, adjectives, and adverbs in a sentence
• Apply grammar knowledge to revise their own writing (not just label parts of speech on a worksheet)

Red flags — signs they need more practice:

• Every sentence in their writing starts with "I" or "The" and follows the same subject-verb pattern
• They put apostrophes in plural nouns ("The dog's were playing" instead of "The dogs were playing")
• They cannot explain why they used a comma — they just sprinkle them randomly
• They can define "noun" but cannot find one in their own writing
• They can combine sentences when told to but never do it independently while writing

When to move on

Grammar is not a one-and-done topic — it spirals through every grade. Your child is ready for fourth-grade grammar when they consistently use compound and complex sentences in their own writing (not just in exercises), when comma usage in lists and compound sentences is mostly automatic, and when apostrophe errors are occasional rather than constant. Perfection is not the standard. Consistent, independent application is.

What comes next

In fourth grade, grammar instruction builds on these foundations:

• Relative clauses — Sentences with who, which, and that ("The girl who lives next door...")
• Progressive verb tenses — "I was walking" vs. "I walked"
• Quotation marks and dialogue punctuation — Correctly formatting conversations in writing
• Prepositional phrases — Expanding sentences with in, on, under, between

The single most important habit to build now: whenever your child finishes a piece of writing, have them read it aloud. If a sentence sounds choppy, try combining. If a sentence is confusing, check the commas. If something sounds wrong, look for the grammar issue. Reading aloud is the most powerful editing tool at any age, and third grade is the perfect time to make it automatic.