1. What is a prefix? un re un means not example: unhappy
A prefix is a word part placed in front of a base word. A prefix usually changes the meaning of the base word. Here's an example:
un + happy = unhappy
The two most common prefixes are
un re 
un means not example: unhappy
Re means again example: redo

2. The spelling of the base word never changes
The spelling of the base word never changes. Simply add the prefix to the beginning of the base word, as in the word unhappy.
The spelling of the prefix never changes. A prefix will be spelled the same no matter what base word it is attached to. For example, if you learn to spell the prefix poly, as in polygon, you can depend on poly to be spelled the same in the words polygraph, polyester, and polygram.
Be aware that double letters can occur. If you add the prefix un to natural, both the prefix and the base word retain their original spelling. The result is unnatural. Take a look at these other words where double letters occur:
il + logical = illogical im + mature = immature il + legal = illegal un + necessary = unnecessary

3. Add the prefix re to the following words
Base add re to base what does it mean
Do redo to do over
Build -
Open -
Think -
Fill -
Pay -
Make -
Move -
Place -
Turn -

4. Add the prefix re to the following words
Base add re to base what does it mean
Do redo to do over
Build - rebuild to build over again
Open - reopen to open again
Think - rethink to think again
Fill refill to fill over again
Pay repay to pay back
Make remake to make over again
Move remove to move over again
Place replace to place over again
Turn return to turn over again or go
back to where it was first

5. Let’s use the dictionary a little
Look up prefixes in the dictionary and examine the entries near the word.
When you look up the word hydro, for example, you’ll see words : hydroelectric, hydropower, and hydrophobia. Discuss how the prefix affects the meaning of the base word.

6. Spelling will never change
The spelling of the prefix never changes. A prefix will be spelled the same no matter what base word it is attached to. For example, if you learn to spell the prefix poly, as in polygon, you can depend on poly to be spelled the same in the words polygraph, polyester, and polygram.

7. Be aware that double letters can occur
Be aware that double letters can occur. If you add the prefix un to natural, both the prefix and the base word retain their original spelling. The result is unnatural. Take a look at these other words where double letters occur. il + logical = illogical im + mature = immature il + legal = illegal un + necessary = unnecessary

8. More examples of double letters when adding a prefix
UN- Other examples: unnoticeable,
IL- illiteracy, immaterial,
IM- immeasurable, immigrant, immobile, immoral,
DIS- dissatisfy, disservice, dissimilar, dissolve,
IR- irreconcilable, irregular, irrelevant, irrestistible, irresponsible,
MIS- misspoke, misspell, misstep

9. Prefixes key Prefix Meaning Example dis- Not dislike Im- Impossible In
Inactive
Mis-
Incorrectly
Misunderstood
Pre-
Before
Prepay re
Again
Redo
Un-
Untied

10. im-not in-not dis-not pre-before re-again un-not Add a prefix to each word in parenthesis ( ) to complete each sentence. 1. Tricia was ________________________ to visit her friend because she had a lot of homework to do. (able)   2. Thomas' teacher told him to ________________________ his essay. (write)   3. He had spelled dozens of words _________________________________. (correctly)   4. Mrs. Sieracki was _________________________________ with the low Social Studies test scores. (happy)   5. Christian _____________________________ his jacket when he came inside the house. (buttoned)   6. Please help you mother _____________________________ the groceries from the car. (load)   7. The students were told they will would not have recess because they ____________ (behaved)   8. The dog was hit often by the man. The dog _________ (liked) the man.   9. The dog ran down the street because the boy left the rope _______(tied)   10. The student was acting __________(appropriate) in the classroom.