The word wall is one of our favorite learning tools. What goes on them and how they are used varies a bit, depending on the grade level, but we've found them to be tremendously valuable to students of all ages.
We typically have high-frequency words, student names, and words we've discovered during our read-alouds that will help us expand our vocabularies on ours, but we love the idea of adding content words.
The key on the upper left-hand side explains the color-coding system. Words for science, math, reading, and writing are added throughout the year. Permanent ink on the whiteboard ensures no accidental erasures will take place and it can be removed at the end of the school year in a variety of ways: with toothpaste, hand sanitizer, Goof Off, dry erase marker over the permanent marker, Mr. Clean Magic Eraser, and fingernail polish remover, to name a few.
The key is to make it fun and to celebrate each time students use the words in their speaking and writing.