Calm your nerves and get him checked out if you are worried (have you spoken with his teachers to see if they think he really has aproblem?)
If he is muddling up his letters he may have slight dyslexia which is NO big deal so don't freak out. If you get in there early enough there are plenty of help and special techniques for helping him and you, so that you don't get stressed out and he doesn't get anxious because he feels he's not achieving the same as his piers
My stepbrother (now 36) was diagnosed with dyslexia at 11 - he has the most amazing memory and you want him on your team for trivial persuit every time.
I live in France and I teach English to primary school kids. Although English is easy gramatically it is not a phonetic language and with the 'gh' sounds (through / rough / night) let alone all the different vowel combinations making different sounds and different vowels making the same sounds as other vowels (cow / plough / sew / know / sea / see )
Ten minutes reading with you each evening may help - at a level that he is comfortable reading.
This may make you laugh
I take it you already know
of tough and bough and cough and dough.
Others may stumble, but not you,
On hiccough, thorough, laugh and through.
Well done! And now you wish, perhaps,
To learn of less familiar traps.
Beware of heard, a dreadful word
That looks like beard and sounds like bird.
And dead-it's said like bed, not bead.
For goodness sake, don't call it deed!
Watch out for meat and great and threat.
They rhyme with suite and straight and debt.
A moth is not a moth in mother,
Nor both in bother, broth in brother,
And here is not a match for there,
Nor dear and fear for pear and bear.
And then there's dose and rose and lose
Just look them up--and goose and choose.
And cork and work and card and ward.
And font and front and word and sword.
And do and go, then thwart and cart.
Come, come I've hardly made a start.
A dreadful language? Man alive,
I'd mastered it when I was five!