B. Foundations of Language · Reading Longer Words and Sentences

Reading Simple, Compound and Complex Sentences

B3.1 B2.5About 40 minutes

Learning goals

I can tell a simple, a compound and a complex sentence apart.
I can find the two ideas in a compound sentence and how they connect.
I can find the main idea and the part that tells when, why, where or if in a complex sentence.
I can read long sentences smoothly, pausing at the comma.
I can say my own simple, compound and complex sentences.

Words to know

simple sentence
A sentence with one complete idea: The fox ran.

compound sentence
Two complete ideas joined by a comma and a joining word like and, but, so or or.

complex sentence
A main idea plus a part that can't stand alone, starting with a word like because, when, if or after.

clause
A group of words with a subject and a verb.

adverbial clause
A clause that tells when, where, why, how or under what condition something happens. It starts with a word like when or because.

subject
Who or what the sentence is about.

Remember from Grade 2

In Grade 2 you learned four kinds of sentences (statements, questions, commands and exclamations) and read compound sentences joined by and, but, so or or.

In Grade 3, you will meet complex sentences: sentences with a part that tells when, why, where or if. Authors use them all the time, so knowing them helps you understand what you read.

Simple sentences

A simple sentence has one complete idea. It has a subject (who or what) and a verb (what they do or are).

The fox ran.
My little sister builds snow forts.
Hockey practice starts at six o'clock.

A simple sentence can still be long, as long as it has just one main idea.

Compound sentences

A compound sentence joins two simple sentences. Each half could be a sentence by itself. They are joined by a comma and a joining word:

The fox ran, and the rabbit hid.
I wanted to skate, but the ice was too thin.
It was raining, so we played a board game.
Do you want soup, or would you like a sandwich?

Complex sentences

A complex sentence has a main idea that could stand alone, plus an adverbial clause that can't stand alone. The adverbial clause tells when, where, why, how or if (under what condition).

Adverbial clauses start with words like these:

when, before, after, while, until, since: tell when
because, since: tell why
if, unless: tell under what condition
where, wherever: tell where
although: tells something surprising or opposite

A complex sentence: an adverbial clause that tells why (Because it snowed) plus a main idea (school was closed).

The clause can move

The adverbial clause can come first or last:

When the bell rang, we went outside. (Clause first: use a comma.)
We went outside when the bell rang. (Clause last: usually no comma.)

Both sentences mean the same thing. When you read, pause at the comma.

Worked example

Let's find the parts of a complex sentence

Read: Although the hill was icy, Theo climbed to the top.

Find the clause starter: Although.
The adverbial clause is Although the hill was icy. Can it stand alone? Although the hill was icy. No, it sounds unfinished.
The main idea is Theo climbed to the top. It can stand alone.
Although tells us something surprising: the hill was icy, but Theo still climbed it.
Read it smoothly with a short pause at the comma.

Main idea: Theo climbed to the top. Adverbial clause: Although the hill was icy (tells something surprising).

Worked example

Let's sort three sentences

Which is simple, which is compound, and which is complex?

The geese flew south.
The geese flew south, and the ducks followed them.
The geese flew south because the weather turned cold.

Sentence 1 has one idea: simple.
Sentence 2 has two ideas that could each stand alone, joined by , and: compound.
Sentence 3 has a main idea (The geese flew south) and a part that can't stand alone (because the weather turned cold), which tells why: complex.

1 = simple, 2 = compound, 3 = complex.

The three sentence types, built from blocks. A compound sentence joins two blocks that can each stand alone; a complex sentence adds a block that can't.

Why it matters for reading

Complex sentences pack in a lot of information. When you read one, ask:

What is the main idea?
What does the other part tell me? When? Why? If what?

This helps you understand cause and effect (because), order of events (before, after) and conditions (if).

Just for fun

Why did the adverbial clause always bring a friend to the party?

Because it can't stand alone!

Hands-on activity

Sentence building blocks

You need: paper strips or sticky notes, a marker, and a grown-up.

Write 4 simple sentences on strips: We wore our coats. / It was cold. / The game ended. / We cheered.
Write clause starters on small cards: because, when, after, if, although, and joining words and, but, so.
Build sentences by joining two strips with a card. Read each one aloud. Is it compound or complex?
Try moving the adverbial clause to the front. Where does the comma go?

Examples: We wore our coats because it was cold. (complex) / It was cold, so we wore our coats. (compound) / When the game ended, we cheered. (complex, comma after the clause).

Your turn

Simple, compound or complex? The moose drank from the lake.

Simple, compound or complex? The moose drank from the lake, and the loon dove underwater.

Simple, compound or complex? The moose drank from the lake when the sun came up.

Find the adverbial clause: If it stops snowing, we will go sledding.

What does the clause tell? We stayed inside because there was a thunderstorm.

Move the clause to the front: We ate popcorn while we watched the movie.

Make a complex sentence by finishing it: After the bell rang, ___.

More practice: warm-up

Which joining word makes a compound sentence: and or because?

Can this stand alone as a sentence? Before we left.

Simple, compound or complex? My cat sleeps all day.

Which word tells when: after or if?

Read with a pause at the comma: When the lights went out, everyone gasped.

More practice: on your own

Find the main idea: Since the bridge was closed, the bus took a different road.

Join these as a compound sentence: The kettle whistled. Mom made tea.

Join the same two as a complex sentence.

What does although tell you in: Although Raj was tired, he finished his book.

Read and explain the order of events: Before we went skating, we sharpened our skates.

Challenge

Which sentence is complex, and why? A) The dog barked, so the baby woke up. B) The baby woke up because the dog barked.

Write one sentence about winter that uses unless.

Split this long sentence into its parts and say what each part tells: While Grandma was making bannock, I set the table because our cousins were coming.

Check your understanding

Quiz

Which sentence is simple?

Which sentence is compound?

In We went inside because it started to hail, the part because it started to hail tells:

Which is not a complete sentence?

Where does the comma go? If you are cold put on a sweater.

Which word could start an adverbial clause that tells when?

For parents and teachers

Big idea: Grade 3 students identify and build simple, compound and complex sentences with adverbial clauses (B3.1). For reading, the key skill is finding the main idea and understanding what the clause adds (when, why, where, under what condition). Pausing at commas in long sentences supports fluency (B2.5).

How to help at home:

When you read together, stop at a long sentence and ask: "What's the main idea? What does the because / when / if part tell us?"
Play "finish my sentence": you say Because it was raining,... and your child finishes it.

Common difficulties:

Thinking every long sentence is compound. Check: can both halves stand alone?
Missing the meaning of although or unless. Give lots of everyday examples.
Writing or saying fragments (Because I was hungry.). Ask: "Because you were hungry, what happened?"

Writing these sentences is also practised in the companion writing unit.