Ultimately this comes down to teacher choice and meeting the needs of your students. Consider a couple of things. First, the purpose of shifting from a word wall to a sound wall is to support students with perceiving the sounds in words and mapping them to known graphemes (speech to print). This process builds the circuitry in the brain needed for reading both regular and irregular words.

If we add words to the Sound Wall, what will our students do? Copy them! The act of copying will not facilitate the mental process of analyzing and internalizing sound/letter relationships. If you want to add a word after it has been explicitly taught, perhaps put the word up for a week or so and then take it down.

After removing the word from your sound wall, formative assessment with retrieval practice will help you determine if your students have successfully internalized the sound/letter relationships for that word.  If your students continue to misread or misspell the word after you take it down, it’s ok! This indicates that they need to go through the process of mapping phonemes to graphemes again.

Note:

Effortful retrieval practice is imperative for learning!  Students should experience reasonable difficulty when learning novel concepts.  For more information about this, consider reading the following:

• Powerful Teaching: Unleash the Science of Learning by Agarwal and Bain (2019)

• Make It Stick: The Science of Successful Learning by Brown et al. (2014)