There is no method for teaching spelling that works reliably with all children, because learning to spell English involves a humungous amount of rote-learning. Different children learn in different ways, and nearly 1 in 2 never become really proficient, no matter what teachers or parents do, because they simply cannot cope with all that memorising.
Some sounds have quite reliable spelling patterns.
Most consonants don't have many exceptions. A few vowel spellings don't either (a, ar, o, oi, -oy, ou, wa, qua for /wo/quo), but most are unpredictable and really just have to be learned word by word.
I analysed the 7,000 most used English words (the sort of words that an average 16-yr-old is likely to have come across) for spelling regularities and irregularities and found 4,217 with one or more unpredictably used letters, from 'said, friend, head' to 'azure' and 'xylophone'.
The best way to learn them is to write a lot and to learn from your mistakes, and use the old LOOK, SAY, COVER, WRITE, CHECK method for the ones that keep causing u trouble.
If it was up to me, i would modernise English spelling and reduce at least some of the most time-consuming inconsistencies, but most people seem to want to continue putting kids throught the torture they had to endure. English-speaking kids world-wide could become much better educated if English spelling became more regular and they did not have to expend so much time on learning to read and write.
Masha Bell