Active and Passive Voice

As young writers work to make their thoughts into sentences that combine into clear essays, they often have a tendency to use too many words in the process.  A common mistake that they make is using passive verbs and writing weak, wordy sentences.  Briefly, in an active sentence the subject of the sentence performs the action of the verb.  In a passive sentence, the subject of the sentence receives the action of the verb.




Examples
Active:  Mrs. Prichard ate lunch.  (The subject is doing the action of the verb.)
Passive:  The lunch was eaten by Mrs. Prichard.  (The verb is receiving the action of the verb.)

Active:  The dog chased the cat.
Passive:  The cat was chased by the dog.

Below are some other on-line resources for further explanation
Purdue's Online Writing Lab
English Club --- has some nice charts
Grammar Girl -- a longer article which addresses stylistic characteristics of active and passive voice.
Wheaton College Writing Center --- includes a section on when to use passive voice.