The mind uses words not only to communicate but also to access concepts. Without an adequate vocabulary for communicating and thinking, our minds are like a teenager's closet: we have to dig through all kinds of crumpled up wads to find what we may or may not have, and if we do find it, it isn't exactly ready to go. Compare this to a meticulously arranged and well-stocked closet. Not only can we find what we need, but all of the "go-togethers" are where we need them. A rich, deep vocabulary allows us to access the tools for thinking—words, words, words!
Explicit and implicit vocabulary instruction has to be ongoing, aggressive, pervasive, recursive, and planned. But happily, the best vocabulary instruction is easy to accomplish if we just remember how words get learned and stay learned. Think of toddlers. The way they learn words through natural language acquisition is exactly how they will always learn words throughout their lives. As toddlers, we learned words through exposure, exploration, examples, enthusiasm, and associations—or what I like to call "4E + A." Likewise, the interaction between the elements in this "4E + A" model can guide vocabulary development in school-age students.
Exposure
Every word that finds its "forever home" in our brains gets there because of repeated exposure in the course of meaningful communication. We need to hear and see new words in a variety of contexts and a variety of forms. For example, if my target word were impress, I would want to support it by using words like impression, impressive, or impressed in different contexts. Although these are all forms of the same word, they are used somewhat differently from each other and reinforce the target word meaning.
Students pick up more information about a new word when it is nestled in a rich context. And bombardment with lots of exposure all at once won't work: the human mind needs exposure over time. Think of how long it takes you to learn the names of your students in a new semester—several days, at least. Going over names again and again on the first day of school will not guarantee that you will learn them. You learn them over time as you distinguish one student from another.
Exploration
Words have depth. We need to exceed brief definitions of words. To really understand and remember a word, we need to spend some quality time with it and get to know its history and family (etymology), subtleties, synonyms, near-synonyms, antonyms, near-antonyms, spelling, and morphological forms. Never teach just one word. Always use the targeted word to reinforce the meaning of related words and the nature of words in general. Be sure to go over how words derive from roots, how they differ ever so slightly from synonyms, and even how their spellings give up clues to their meanings. I think of a word as a little archeological specimen, amenable to exploration and discovery about the world in which it lives now and the worlds in which it has lived.
Consider these examples: We use the word register to refer to making ourselves official members of a group. Register can be said to be a great-great-great grandchild of the word regal, meaning "king or queen like." The word second is known by all English speakers. But if we relate it to its cousins, sequence, consequence, and consecutive, we understand that these words are connected via a common ancestry: sequ- means "follow." The word second simply changed its spelling from that of its relatives!
Examples
Many of the words we teach represent abstract concepts. Abstractions are understood through concretions, hence the importance of examples in teaching a word. Most of the words in your vocabulary that represent abstract concepts got there not because you were taught a definition, but because you attached examples of the concept to the words. Examples allow for visualization, association, and something called concept attainment—or the carving out of features for a concept. For example, society is in the process reshaping and redefining the concept of marriage to include same-sex couples, accepting (or not) the example of two men or two women and their relationship as being included (or still excluded) in the concept of marriage.
Enthusiasm
We should teach everything with enthusiasm, so why is it necessary to stipulate that we need to teach vocabulary with enthusiasm? Unfortunately, teachers often present vocabulary as a disembodied list of "this week's words" or desultory assignments to "look up these words, write the definitions, and use them in a sentence." Cease and desist with the dreary fill-in or circle-the-correct-choice exercises! Engage students in word games and puzzles, tell stories about words, model your interest and joy in learning new words or extending your understanding of familiar ones. Be open to questions about connotation and the changing nature of language. Introduce neologisms (like selfie) and buzzwords. Explore slang, archaic words, and expressions. Be a word watcher of terms that recur in popular media, and share your curiosity and discoveries.
Associations
The brain is a hyperlinked file cabinet that is capable of retrieving information from multiple "drawers." If a word is "filed" in only one drawer—that is, if we associate it with only one thing, such as a brief definition—then it is a needle in a haystack. What if you were to bury in a haystack one clue about the needle's location? Well, you would then have to hunt for that single clue. But what if you were to stash multiple clues in various locations in the haystack? That would make it much more likely that you could reach in, grab one of the many clues, and retrieve the needle. That is what we do by having multiple associations—sensory clues, experiential clues, cognitive clues—for words we learn. If I associate the word detour with a time when I had to detour around a construction site, then I have an experiential association with the word. But if I also associate it with the word tour and the prefix de-, which can mean "away from," then I have two ways of accessing it in my haystack of a brain: through experience and through analysis.
With exposure, exploration, examples, enthusiasm, and associations in mind, it's easier than you think to help students grow their vocabularies. Elevated academic language matched with these supports draws on how toddlers acquire language—our first and best model for learning words.