I think children's abilities to just know what's what and what isn't are seriously underrated.
Going by my own kids and grandkids, having taught some very bright kids A level as well as some bottom sets in comps, along with some slow readers in primaries,
I would say under and over, yes and no.
I keep trying to find better ways of explaining what the main English spelling problems are. Does this following help?
By analysing the 7,000 most used English words for spelling regularities and irregularities, I found that roughly 4 words in every 7 contain some unpredictable letters, like ?friend? or ?eight? (cf. end, date):
English has 91 main spelling patterns, 80 of which have exceptions, but
the main retardants of progress with learning to write are the following 10:
973 words with inconsistent consonant doubling,
(poppy ? copy).
459 unpredictably spelt /ee/
(speak, seek, shriek, seize, scene...key, ski, quay...)
196 irregular long /oo/,
(scoop, soup, move, blue, shoe, flew, through...).
156 variants for long /o/
(stole - coal, bowl, poll).
154 surplus ?e endings
(are, have, imagine, delicate, promise ?
car, chav, boffin, acrobat, tennis)
150 unpredictable
(her bird turned early)
102 variants for
(date ? great, straight, eight, gait)
68 irregular short
(cut - couple, come, compass, does, blood)
67 irregular
(bed - said, head, any, friend )
45 irregular
(sit ? pretty, busy, women, build, crypt)
Those 10 irregularities make 2,370 words tricky to spell. They slow reading progress too, because many of the variants are used for more than one sound (e.g. trouble, group; said, laid; threat, great).
Exceptions to the other 70 spelling patterns affect only 1,331 words between them. Many of them also occur in the endings of longer or less common words (ordinary ? archery; potter ? actor; present ? peasant) and are learnt mainly in the later school years, with less impact on overall literacy progress. The greatest impediments are posed by the irregular spellings of words which children meet and need to use in their own writing in the early years, such as ?said, one, friend?.
The greater the number of words with variant spellings which has to be memorised, the longer they take to learn, but the strength of the pattern from which they diverge has an effect too. Because the long /oo/ sound, for example, is spelt in only 95 words, while 101 have other spellings, all the spellings for it have to be learned word by word.
One of the numerically relatively small irregularities takes much learning too. The short /oo/ sound of ?foot, put, should? occurs in merely 35 words (as spoken by most people), but its spelling is exceptionally tricky because it has no unique pattern of its own. All the spellings used for it are more common for other sounds (foot ? boot, root...; put ? but, cut...; should - smoulder, shoulder...; wolf ? wobble, wombat...).
The biggest spelling difficulty cuts across several sounds. The greatest source of English spelling errors are the 334 sets of different spellings for homophones, such as ?their /there? and ?it?s /its?.