Words Their Way, check out the foundational text by the same name. To see an example of the developmental spelling inventory, check out this tutorial from 
Pearsontraining.
In the past few years, I have tried different things, but worked to simplify the process of having too many groups, word lists, and activities for students to complete. I have also worked to find routine activities that remind students of the purpose of word study~that the spelling learning should transfer into our actual writing! I have found that students' spelling deteriorates when word study is dropped from the classroom (maybe students think you don't think spelling is important at that point?) and that if I can get my routines together, students actually have a lot of fun during word study.
Keep in mind that the routines and ideas I describe below are from the upper elementary perspective. Of course, modifications and scaffolding may be necessary for lower grades and weaker spellers.
Tip # 1: Stop planning Mon, Tues, Wed, Thurs, Fri routines and think of your word study activities as a cycle. Students cycle through all activities for each word list. This shift in thinking helped me tons--our schedule gets interrupted, so teaching students "This is what we do on Monday, Tuesday, Wednesday," was really always an issue. Now, I have a seven day cycle of activities for students, including a few whole group days where we work together. How do I keep up with where we are? I have a chart showing each groups' assignment for the day. We move a sticky note that says "We are Here!" each day. This also gives us the freedom to have "off" days where we do something else with our word study time.
Although we might take a week and a half to cycle through the activities
 for one word list, we value word study more because we know ALL of the 
routines are going to happen for that word list. When we are almost at 
the end of a quarter or a long break, I start staggering groups out of 
word study. 
Here's my current word study cycle of activities (and it feels "successful" most of the time):
 Day 1} Complete "Blind" Word Search
 Day 1} Complete "Blind" Word Search and try to deduce current word sort rule or pattern. If you are familiar with 
Words Their Way,
 then you know that a "blind sort" is an activity where students sort 
the words into categories (and write them down) as they hear them called
 out. It's called BLIND because they are not looking at the words. By doing this "blind searching" through a word search, students 
have a fun way of figuring out their word pattern focus for the word study cycle. 
The word search WORD searching is an engaging, fun way for students to 
discover some of their words and 
sharpen their ability to recognize 
words that are spelled correctly (a major key to spelling improvement). 
Students also demonstrate their understanding of sorting by sound and/or
 look when they record the words they have found into categories. (Students have the word searches glued into their notebooks and MUST record the words as they find them by SORTING the words into categories)
Tip # 2: Once you assess students and decide which lists they will start with, make copies of the word searches they will need for the quarter and spend a session helping students glue the word searches into their notebooks. I save 2-3 pages between each word search for word work and for "Meet with the Teacher." Remind students to keep the word searches in order as they glue them!
Tip # 3: You can work with your lower group before they do Word Search day. This
 gives them exposure to the word patterns they will be working with and 
hopefully a boost of confidence as they search for their words. If you 
have younger students and want them to have a copy of the words, just 
give them the word list from the Word Study books, but I strongly encourage you to consider giving
 them a few words to get them started and then have them search for the 
patterns, rather than spoon-feeding them the whole list.
 Day 2} Meet with the Teacher
Day 2} Meet with the Teacher (includes sorting words, discussing word patterns/rules and word meanings, etc.)With average/higher groups, I ask what words they found in their word search and we sort them into categories on a white board. Sometimes I will provide them with other words they should have found, but hearing what their group members found gives them clues about what else to look for.
Tip # 4: The lower groups just need practice, practice, practice, and immediate feedback. When these kiddos meet with the teacher, I give them a white board, marker, and eraser and fire off words at them from the list they are on and from previous lists. We often have to focus on short sounds vs long sounds, words with double vowel patterns, and making sure we have represented all of the sounds found in the words.
Tip # 5: For your struggling spellers, try using compound words that still fit the patterns they are studying. This allows them to practice DOUBLE the words and will allow them to feel like they are working on words just as large as other groups in the class.