It may seem surprising, but we only come across one major cause of spelling difficulty, which is a poor reading strategy.
Thousands of children spend hours learning spelling lists, only to find they have dissolved in their head a week later. It is like pushing water up hill.
The core to good spelling is decoding as you read. So the children who cannot spell are almost always sight reading the words (what we call Optilexia).
Because they are not developing a subconscious map of spellings as they read, they have no map of spellings when they write.
To illustrate how subconscious our spelling is let me ask you this; "If the right answer was worth a trip around the world, would you rather work out a spelling in your head or write it down and read out what you have written?"
Most of us would definitely go for the latter option, because it allows the spelling to come out from our subconscious. As soon as we start to think about a spelling, we have to operate in our conscious, declarative memory. But that is not where our knowledge of spelling patterns is stored and so you tend to become less and less sure of a spelling in that way.
Therefore, the only way to build a foundation for good spelling is through good reading practice. And the easiest way to do that is through Guided Phonetic Reading.