Spelling words and word wall words have different purposes. Word wall words are typically basic, common words that are used often in writing and therefore it's important that children learn to spell them correctly. In the early grades, the word wall would have words like "the," "and," "that" and "ours." As the year progresses, common synonyms might be added, such as "there" and "their" and "your" and "you're." Spelling words expand vocabulary by adding to the words children can spell correctly. Word wall words can be spelling words at first, but later spelling words might come from a book the class is reading or a history lesson.
Word wall words will be used often in writing. Many of them will be used multiple times each day. They are basic words, not the most difficult words, so all the children in the class should be able to spell and use them correctly in their writing, regardless of the differences in the children's language arts abilities. Spelling words, however, are more often tailored to children's abilities. A teacher often has three or more spelling lists for children with different levels of spelling ability.
Spelling words are usually studied for one week, with a spelling test given at the end of the week. The next week, a new spelling word list is given. When teachers have individual spelling lists for each child, the words missed on the spelling test may be carried over to the next week's list, but the rest of last week's list is replaced with a new list of words. Word wall words, on the other hand, stay up on the wall for months or even for the year, so children can refer to them when they are writing. This has the added benefit of showing children how far they have progressed from the easy everyday words to the more difficult common words they have learned to use.
Word wall words are often words that don't follow conventional spelling rules. They just have to be memorized and remembered, reinforced through frequent usage. Spelling words are sometimes exceptions to spelling rules, too, but more often they are words with a common theme or a that share spelling patterns.