Children need to be encouraged to use their knowledge of word parts, specifically prefixes, suffixes to pull an unknown word apart and determine its meaning. And just as you don’t try to teach your child every unfamiliar word in a story, it is helpful to focus on learning only the most important of the hundreds of affixes and roots. If your child comes to know these really well, he will be able to add substantially to his reading vocabulary. Fortunately, only a relative few of these word parts occur with any real frequency: Just twenty prefixes account for 97 percent of all words with prefixes found in English schoolbooks, and nine of these prefixes account for 75 percent of all prefixed words. Here are the most common ones: