Grade by Grade
B. Foundations of Language · Reading Longer Words and Sentences

Word Parts I: Prefixes Change the Meaning

B2.3 B2.4About 40 minutes
Learning goals
  • I can find a prefix and the base word in a longer word.
  • I can tell the meaning of prefixes like non-, over-, under-, in-, im-, sub- and mid-.
  • I can use a prefix and a base word to figure out what a new word means.
  • I can check that a prefix is really a prefix by making sure the rest is a real word.

Words to know

morpheme
The smallest part of a word that has meaning. Unlock has two morphemes: un + lock.
base word
The main part of a word that can stand by itself, like lock in unlock.
prefix
A word part added to the front of a base word. It changes the meaning.
meaning
What a word or word part tells us.

Remember from Grade 2

In Grade 2 you learned these prefixes:

  • un- and dis-: not, or the opposite (unhappy, dislike)
  • re-: again (reread)
  • mis-: wrongly (misspell)
  • pre-: before (preheat)
  • uni-, bi-, tri-: one, two, three (unicycle, bicycle, tricycle)

In Grade 3, you will learn more prefixes and use them like keys to unlock the meanings of new words.

Words are built from meaning parts

The smallest part of a word that has meaning is called a morpheme. A prefix is a morpheme. A base word is a morpheme too.

When you see a long word, look for the parts. Then add the meanings together.

under+water=prefix: belowbase wordunderwaterbelow the water
under (prefix meaning below) + water (base word) = underwater: below the water.
PrefixMeaningExamples
non-notnonstop, nonfiction, nonsense
over-too much, or aboveovercook, overflow, overhead
under-below, or too littleunderground, underwater, undercooked
in-notincorrect, incomplete, invisible
im-not (used before m, p or b)impossible, impolite, impatient
sub-under, belowsubway, submarine
mid-middlemidnight, midday, midweek
New prefixes for Grade 3
Worked example

Let's use a prefix to find the meaning

Read: The bus went nonstop from Toronto to Kingston.

What does nonstop mean?

  1. Find the prefix: non-. It means not.
  2. Find the base word: stop.
  3. Add the meanings: not + stop = not stopping.
  4. Check in the sentence: the bus didn't stop on the way. Yes, it makes sense.

nonstop means without stopping.

Worked example

Let's compare two prefixes

What is the difference between overcooked and undercooked?

  1. Both have the base word cook and the suffix -ed.
  2. over- means too much. Overcooked food was cooked too much. It might be dry or burnt.
  3. under- means too little. Undercooked food was not cooked enough. It might still be cold or raw inside.

The prefixes are opposites, so the words are opposites: too much vs. too little.

undercookedunder- = too littlecookedjust rightovercookedover- = too muchcooking time
under- and over- are opposites: an undercooked cookie was cooked too little, and an overcooked one was cooked too much.

Is it really a prefix?

Some words start with letters that look like a prefix, but they aren't. Cover the "prefix" and look at what's left. Is it a real word that fits the meaning?

  • unlock → lock ✅ (prefix)
  • uncle → cle ❌ (not a prefix)
  • refill → fill ✅ (prefix)
  • ready → ady ❌ (not a prefix)
  • invisible → visible ✅ (prefix)
  • inside → side ✅, but here in- means in, not not! Always check the meaning in the sentence.

Prefixes help you read, too

When you spot a prefix, you can read it as one chunk. Then you only have to read the base word.

im | pa | tient → im- + patient → im-PAY-shunt. It means not patient: not able to wait calmly.

Worked example

Let's read and understand a sentence

Read: The submarine travelled underwater at midnight.

  1. submarine: sub- (under) + marine (about the sea). A boat that goes under the sea.
  2. underwater: under- (below) + water. Below the water.
  3. midnight: mid- (middle) + night. The middle of the night, 12 o'clock at night.
  4. Now read the whole sentence smoothly.

The sentence tells us a boat travelled below the sea in the middle of the night.

Just for fun

Funny but true: The word impossible has a secret message hiding in it. Split it a new way and it says I'm possible!

Hands-on activity

Prefix flip cards

You need: 8 index cards or paper squares and a marker.

  1. On 4 cards write prefixes: non-, over-, under-, im-. On 4 cards write base words: sense, flow, ground, possible.
  2. Match each prefix to a base word to make a real word: nonsense, overflow, underground, impossible.
  3. For each word, say the meaning by adding the parts: "im- means not, so impossible means not possible."
  4. Try silly mixes too, like undersense or imflow. Are they real words? (No! A word is only real if people use it. Prefixes are clues, but you always check.)
  5. Hunt for one prefix word in a book or on a sign.

Your turn

1

What does non- mean? Read and explain nonfiction.

2

What does overflow mean?

3

Read impolite. What does it mean?

4

Find the prefix and base word in incomplete.

5

What does midday mean?

6

Is un- a prefix in uncle? How do you know?

7

Read: The impatient dog waited by the door. What does impatient mean?

More practice: warm-up

1

What does under- mean?

2

What does mid- mean?

3

Find the prefix in subway.

4

Add a prefix to correct to mean not correct.

5

What does redo mean?

More practice: on your own

1

Explain the difference between overdressed and underdressed for a snowy day.

2

Add im- or in- to make each word mean not: possible, visible, perfect.

3

Read: It was nonsense to wear sandals in a blizzard. What does nonsense mean?

4

Which word has a real prefix: reread or reach?

5

Use underground in a sentence about an animal.

Challenge

1

Read misunderstand. Find the prefix and base, and say what it means.

2

Make two new words from the base word heat using two different prefixes. Explain them.

3

Read: The midweek game was unpredictable. Explain midweek and unpredictable.

Check your understanding

Quiz

1.

What does non- mean?

2.

What does undercooked mean?

3.

Which word means not possible?

4.

In which word is re- a real prefix?

5.

Midnight means:

6.

A submarine goes:

For parents and teachers

Big idea: Grade 3 students use morphemes (bases, prefixes, suffixes) to read and understand words (B2.3) and to figure out new words in context (B2.4). This lesson adds the prefixes non-, over-, under-, in-, im-, sub- and mid- to the Grade 2 set.

How to help at home:

  • Ask "What's the base word? What does the prefix add?" when you meet words like unfair, overtime, rewind.
  • Play "prefix tag": you say a base word (happy), your child adds a prefix (unhappy) and says the meaning.

Common difficulties:

  • Seeing fake prefixes (uncle, ready, interesting). Teach the "cover and check" step.
  • Mixing up in- meaning "not" and in- meaning "inside" (invisible vs. indoor). Always check the sentence.
  • Forgetting im- before p, b or m. This matters more for spelling, but noticing it helps reading too.