Here the words that J has gotten wrong are spelled out on old church concert tickets.
The letter he got right are in black.
The letters wrong are in green (whatever color you want.)
The sneaky, tricky, silent letters are given drawings, more colors, etc. to make them stand out.
As you can see above refrigerator has many different things going on. We started out with a little bit of visual velcro, and have added as needed. The green are the misspelled letters, the blue wavy lines are cold air under them. The red divides the sections of the word. The red around the "ator"are supposed to be lips "eating" that part of the word "ATE or". J drew the gator - ator. The orange are the letters he kept forgetting time after time.
Any visual velcro you can think of helps. J comes up with his own many times. Right Brainers are very visual and take pictures with their brains.
Also, here's how we practice. After writing the words. I hold them up. (My elbow is on the table, my hand is up in the air.) "Look and the first and the last letters and any funny letter." I instruct. After a few seconds. I put the card down. J keeps looking up at his "screen" to see the word in his head. We do this up and down with each word until he gets it. (Usually now more then five times.) We try to do this with each word everyday. The words that he doesn't get right I keep in and the right ones I take out at the end of the week.
These spelling words are kept in a baggie clothes pinned to our dry erase board. We also keep our Sentence rules, -ing rules there too. We use some visual velcro here too.
I hope this has helped. It may seem like a lot of work on your part, but it is fun and they really get into it. You won't have to do this forever. They will start to get it and make pictures for themselves in their mind automatically.
We have done the visual velcro with C too. She uses it a lot in test taking, review.