My ds reads some words backwards eg he reads dog as god and was as saw.
This can quite often indicate that a child has poor eye tracking skills. English words are read from left to right but this doesn't come 'naturally'; it has to be practised so that the eyes' tracking muscles can be 'trained' and strengthened. The most effective way to do this is by teaching children to sound out and blend all words from left to right all through the word. Problems with eye tracking can usually be traced back to initial reading instruction. 'Mixed methods', which teach several strategies for word identification, don't give some children enough consistent practice in reading words from left to right and so left to right tracking isn't properly developed.
If the eye muscles are weak for L to R tracking you might find that asking a child who reads words the 'wrong way round' to consistently read words from L to R causes them actual stress as they have to exercise weak muscles to do so. They rub their eyes a lot, maybe complain that it's giving them a headache, get nearer and nearer to the print so that their nose is practically touching the page... I'm afraid that the solution to the problem is more practice..little and often, of course, to avoid causing undue stress.
Strategies which may have been taught and which may have contributed to this problem are learning words as 'wholes' (the dreaded 'sight words') and looking for clues to words in pictures. These both interfere with L to R tracking. The more dependent a child becomes on these strategies the less 'correct' exercise the tracking muscles get.
It's worth considering...
With regard to spelling, it is essential that a child knows that the letters in words represent the word's component sounds and that to spell a word the first step is to identify the sounds, then ensure that every sound in the word has been spelled. Depending on learning a string of letters is difficult as letters can easily be missed or transposed because the child a) can't remember them all and b) doesn't understand what their function is in a word.
So it's also worth considering how your child was taught to 'learn' spellings. Was it by learning 'letter strings' or by breaking words into 'sounds' and spelling the sounds? The method they use may well have a bearing on their difficulties.