In order to be an effective word study teacher you will need many tools in your tool cabinet.  Gone are the days where teaching spelling simply required one tool: a drill. If you simply ask students to memorize words (just use the "drill") they will never learn all the words they need to know to write and communicate well. It is not only impossible, but impractical to think that anyone can memorize all the words in our language. Memorization plays an important role in a word study program, but memorization alone is not enough. Generalizing patterns and principles of spelling is equally important. 

The best place to begin effective spelling instruction is with assessments to help you clearly identify developmental stages of spelling for each student.  There are many tools you can use to determine spelling stage.  One of the more systematic and common tools is a developmental spelling inventory like those published in Words Their Way and Word Journeys.

Here are the assessments I have adapted from Words Their Way. We use these in our district for grades K-8. These tools serve as a way to MEASURE developmental progress and inform instructional decisions.