Teaching Sentence Structure to Third Graders

By third grade, our students can write sentences. They know they need a capital letter at the beginning and a punctuation mark at the end. But their writing often sounds like this:

"I went to the park. It was fun. I played on the swings. My friend was there. We played tag."

Simple sentences. One after another. Like a list of facts. It technically works, but it doesn't flow. Third grade is when we teach kids to make their writing sound better, more varied, more interesting, more like real writing.

What Third Graders Should Learn About Sentences

According to Common Core L.3.1, third graders should:

• Write simple, compound, and complex sentences
• Use conjunctions (and, but, or, so, because)
• Vary sentence length and structure
• Produce complete sentences (recognizing and correcting fragments and run-ons)

That's a big leap from second grade. Let's break it down.

The Four Sentence Types

1. Statements (Declarative)

Tell something. End with a period.

"The dog played in the yard."

Honestly? The kids who struggle most with this often surprise you a month later.

Kids already know these. They write them every day.

2. Questions (Interrogative)

Ask something. End with a question mark.

"Did the dog play in the yard?"

Review from 1st-2nd grade. Most third graders have this down.

3. Commands (Imperative)

Tell someone to do something. End with a period (or exclamation mark for strong commands).

"Throw the ball to the dog."

This one surprises kids. "Where's the subject?" The subject is "you" (understood). That's a fun mini-lesson.

4. Exclamations (Exclamatory)

Show strong feelings. End with an exclamation mark.

"That dog runs so fast!"

The difference between an exclamation and a statement with an exclamation mark is subtle. For third grade, don't overthink it.

Activity: Write 12 sentences on cards. Kids sort them into four piles. Then they write one of each type about the same topic.

The Big Upgrade: Compound Sentences

This is the game-changer for third grade writing. Compound sentences combine two simple sentences with a conjunction.

"I like pizza" + "I don't like mushrooms" = "I like pizza, but I don't like mushrooms."

The FANBOYS

Teach the seven coordinating conjunctions:

• For (because/since)
• And (addition)
• Nor (neither)
• But (contrast)
• Or (choice)
• Yet (contrast/surprise)
• So (result)

Realistically, third graders will use four of these regularly: and, but, or, so. That's fine. Mastering those four is enough.

How to Teach Compound Sentences

Sentence combining. Give kids two simple sentences and a conjunction. They combine them.

• "The sun was out." + "We stayed inside." + BUT = "The sun was out, but we stayed inside."
• "We can go to the park." + "We can stay home." + OR = "We can go to the park, or we can stay home."

Start with guided practice. Do 5 examples together. Then let kids try independently.

Don't forget the comma! Compound sentences get a comma BEFORE the conjunction. "I ran to the store**,** and I bought milk." This takes weeks of practice to become automatic.

Fragments and Run-Ons

Fragments

A fragment is a sentence that's missing something. Usually a subject or a verb.

• "Running to the store." (No subject. WHO is running?)
• "My big sister." (No verb. What did she DO?)

Activity: Write fragments on the board. Kids fix them by adding the missing piece. Make it a game: "Fix That Fragment!"

Run-Ons

A run-on is two sentences smashed together with no punctuation or conjunction.

• "I went to school I ate lunch I played outside." (Three sentences pretending to be one)

Activity: Give kids run-on sentences. They break them apart with periods or combine them with conjunctions.

Varying Sentence Length

The secret to good writing isn't always using long sentences. It's mixing lengths.

Short sentence. Then a longer one that adds details and description. Then short again. This creates rhythm.

Read a paragraph from a good children's book aloud. Count the words in each sentence. Notice the variety. "The author uses 4 words here, then 12, then 6. That's what makes it sound interesting."

Activity: Write a paragraph where every sentence is exactly 5 words. Read it aloud. It sounds weird, right? Now rewrite it with varied lengths. Much better.

Sentence Expanding

Start with a basic sentence. Make it grow.

• "The cat sat." (subject + verb)
• "The orange cat sat." (add adjective)
• "The orange cat sat on the mat." (add where)
• "The orange cat sat on the mat after dinner." (add when)
• "The fluffy orange cat sat quietly on the old mat after a big dinner." (add details everywhere)

This activity shows kids that sentences can grow. They don't have to stay simple forever.

An Anchor Chart Worth Making

Create a classroom poster:

Simple Sentence: One complete thought. "The bird sang." Compound Sentence: Two thoughts joined by a conjunction. "The bird sang, and the cat listened." Fragment: Missing something. "Singing loudly." (Fix it!) Run-On: Too many thoughts, no break. "The bird sang the cat listened." (Fix it!)

Keep it visible all year. Point to it during writing time.

The Connection to Writing

Sentence structure isn't just a grammar lesson. It directly improves writing quality. When kids can vary their sentences, their stories, reports, and essays all get better.

Encourage kids to reread their writing and ask: "Do all my sentences start the same way? Are they all the same length? Can I combine any of them?"

Those three questions will transform third grade writing.

Keep Reading

• Creative Writing Prompts for Third Graders That Actually Get Kids Writing
• Idioms for Kids: 100 Common Idioms With Meanings + Worksheet

Start Small

This week, focus on one skill: combining two sentences with "and" or "but." Practice it every day during writing time. Next week, add "or" and "so."

By the end of the month, compound sentences will feel natural.

For daily practice, our 3rd grade sentence structure worksheets cover all four sentence types, compound sentences, fragment fixes, and sentence expanding exercises.