i think the first stage is to have your son diagnosed and a report issued by an independent qualified assessor. This will ensure your sons school recognises the condition and will give him additional time to complete work in class (or for exams, if applicable). Although there is no cure (and it is by no means a disability, as you will find that your son has other attributes that compensate), they can give advice on how to deal with this and can recommend internet sites with spelling activities or inspirational software). Your sons school should be able to recognise someone to assess your son.