the difference in spelling ability between DS1 and DS2 is marked.
Children vary enormously in their ability to learn to spell English, irrespective of how they are taught, depending mainly on whether they have a good visual memory or not.
Beyond a very elementary level, phonics is totally useless for learning to spell English.
The trickiest part of English spelling are the 335 heterographs like there/their and hear/here. Phonics is completely useless for learning to spell those.
The second biggest challenge is consonant doubling (copy poppy, very merry, shoddy body). Doubling is used predictably for keeping a stressed short vowel short when short words are made longer
by adding -ed, -en, -er, -ing, -y or –ish
(e.g. fat - fatted, fatten, fatter, fattish... batting, batty)
to distinguish them from ones with a long vowel
(bate - bated, bating).
In longer root words, consonant doubling is completely unpredictable:
423 words use them systematically (e.g. mellow, yellow),
554 don't use them (e.g. melon, melody) and
195 words have needlessly doubled consonants (e.g. satellite, accommodation) after unstressed vowels.
The numerically third biggest problem are the 352 words with an ee sound (speech speack shriek...).
I analysed the spellings of the 7,000 most used English words and found that 80 of the 91 main English spelling patterns have exceptions -
i.e. 4,219 of the 7,000 most HF words contain one or more phonically unpredictably used letters which simply have to be learned one by one (mANy, frIend, heAd, blUE, shOE, flEW).
Masha Bell