An excerpt from Reading Rockets
Fluency is defined as the ability to read with speed, accuracy, and proper expression. In order to understand what they read, children must be able to read fluently whether they are reading aloud or silently. When reading aloud, fluent readers read in phrases and add intonation appropriately. Their reading is smooth and has expression.
Children who do not read with fluency sound choppy and awkward. Those students may have difficulty with decoding skills or they may just need more practice with speed and smoothness in reading. Fluency is also important for motivation; children who find reading laborious tend not to want read! As readers head into upper elementary grades, fluency becomes increasingly important. The volume of reading required in the upper elementary years escalates dramatically. Students whose reading is slow or labored will have trouble meeting the reading demands of their grade level.