A simple method to practice spelling words that can be used over and over again is putting a small amount of hair gel in a plastic storage bag and sealing it, then your child can trace the letters with his finger through the gel.
Hair Gel Lesson
|hair gel (about a cup)|
|gallon size plastic storage bag|
|spelling words from group B|
I also found this great looking product through Orton Gillingham that is amagnetic gel that looks very similar to the hair gel. It looks cool so if this is an effective way for your son to practice you may want to ask him if he would like to try it out. It might be something he enjoys!