I really like the All About Spelling method of teaching. I'm actually using it for my 6yo right now, but I really think it is absolutely NOT too "young" for older kids. The lessons are well-designed and thorough, and they give even me as the teacher a better understanding of what the rules for the English language are. I've always been a very good speller & reader, myself, but I'm honestly learning a LOT about the "whys" of what sounds each letter makes in each different situation. This book gets extremely specific on learning the actual general rules of use so that you can employ those rules in reading more and more convoluted words.
I actually don't have my 6yo do any copywork - he does straight writing of sentences, deciding on his own how to spell the words. When he's done, I just pick which words need help and ask him to tell me what the appropriate rule is for that sound. Once he's recited the rule, he is immediately able to correct his own work.
For example - he is having problems on when to use "k" vs "ck", so I ask him to tell me what the rule for using "ck" is (to use it after a short vowel). I then have him point out the vowel and tell him if it is long or short. His response might then be "oooooh, yeah, it's a short vowel so I use ck". We also have spent a lot of time working on the silent "e" - how it makes the word "open", and an open word generally has a long vowel sound (no is open, not is closed). I like that it then ties multiple previous lessons together as you go along - my 6yo can work out that in a "vowel-consonant-e" word that has a hard "k" sound, you HAVE to use "k" rather than "c" or "ck" (like). After all, we learned "ck" is only used after a short vowel (which you don't have in an open word) and we learned "c" says sssss before e,i&y (so that wouldn't work). The joy, though, is that HE actually truly knows these rules & I just have to remind him to think of them and to pick which ones apply!
Sorry to go on - I just wanted to make it clear that while the All About Spelling books can be used for younger kids, I believe it can totally provide a good foundation for older kids as well. As I recall, the website indicates it is used for beginning spellers through older (and even adult) spellers needing remedial work.