I love my daughter's spelling book. It's called Building Spelling Skills Book 3 by Christian Liberty Press. While my daughter was attending 3rd grade at our local Christian school she was coming home with 15 spelling words to learn each week and they didn't seem to follow any sort of pattern.
This curriculum has her learning 20 words each week and it follows sound patterns. I feel like she is being adequately challenged and reading better because she is able to sound out words according to their patterns. Each day's lesson is planned out for you in the guide.
Each school year has 40 weeks and this book covers 36 weeks. I find that to be perfect because you never know when your kids is going to get sick or you are going to go on vacation, etc. So if you miss one week per semester you will still finish the book on time.
I highly recommend this book if your child is good at basic spelling and is up to learning and memorizing 20 new words per week.