High frequency words are words that occur often in the texts that students read. Since they show up often, students need to have these words mapped into their minds securely. These words are sometimes called sight words (know by sight), popcorn words (pop into our head) or heart words (know by heart). For each high frequency word, we map the sounds in the word to the spelling used in the word. This helps our brains recognize these words more easily as well as other similar words.
Our list of high frequency words was chosen based on the decodable books we are using. It contains only words that either use a pattern that hasn't been introduced, yet, or is an irregular word (i.e. doesn't follow all of the phonics rules). High frequency words (e.g. up, can, with) that follow the phonics rules introduced in Kindergarten are not on our list.