Give the assessment test first
Our school, too, uses a set list of words that is often too easy for some of the children. I always give the Words Their Way test three times a year just so I can track the development of each child's spelling progress. (I use the primary word list.) For those students scoring in a higher level than our program is currently focusing on, I choose words from their stage. I get the words right form the Words Their Way book (at the back) and make up word sorts for them. (a template is there as well) I then look for other activity sheets that focus on that particular skill for them to complete throughout the week. I try to group children together so they can work in small groups. Sometimes the weekly testing of their words can get tricky with individual spelling lists, but a parent volunteer would be ideal for this.
I recommend keeping a binder of all the worksheets and the masters of word sorts you create so you can use them again. Good luck!