The posting of this SWI investigation is inspired by Mary Beth Steven's amazing blog post "Please don't judge me on my looks!" It was not explicitly linked to Martin Luther King day -- but as the post came January 15, an image and link to something about this important holiday popped up at the side of the post. That happenstance raised the idea of that this post could be used as a jumping off point for a study of the ideas behind this day in a number of ways.
I recommend reading her post for a great analysis of SWI instruction and how it contrasts with more typical spelling instruction. Also, among the words in the family of the bound base <fer> from the Latin root fer(re) for "bring, bear" that she addresses are these words: <differenntly>, <offer>, <suffering>, and <prefer>. I suspect teachers and students could find ways to draw on these and other relatives of this family to compose thoughts about what this day is about. If you actually paste the Latin word ferre in the search engine of Etymonline, you will find some fascinating and surprising words that could be considered in the context of writing/discussing MLK day such as: <infer>, <defer>, <vociferous>, <confer>, and believe it or not <legislator> and <elation>!
This linking of content and SWI reminded me of a document I made at the Nueva School last year to support study of this day. You can download that document HERE. See a screen shot of some of the word families that might provoke some interesting study of the concepts relevant to Martin Luther King day, and words to help understand and study this topic.