In one of my intervention groups, we are working on hard and soft "c" and "g" sounds. When I was teaching in third grade, we did this yearly as a spelling rule.
We began with Hard & Soft C and filled out all the words that I dictated to them and categorized them as hard or soft. Then, I left it up to the students to identify the patterns they noticed and we added it to the little (obviously TOO little!) definition box at the top.
Next, we did the same thing with G, and the kids really got it! It's a super simple anchor chart, but the kids have been referencing it already.
In my other intervention group, we are working on R-Controlled Vowels, so look for a similar anchor chart for that soon!