Other issues beyond reading and writing that can indicate dyslexia include problems with a sense of time, personal organisation, map reading and other things associated with higher executive function. A dyslexic in a non-literate society is likely to still be known as the most scatty one in the village for example 
Three underlying dyslexia causes as dollfrog said -
Visual - go to a proper optrometist (not the high st vision test) and get stuff like visual tracking issues identified - there are excercises a child can do that can signficantly improve things for this group. Some children may be prescribed tinted lenses etc to help also.
Attention - a pead will identify this and at the extreme end a diagnosis of add or adhd may be given. Many parents have made some improvements in this area by dietry changes.
Auditory Not just the standard hearing test. How well does the child process what he hears? This is a tougher nut than visual issues to resolve or cure, partly due to the lack of available specialists to help either NHS or private, but again there are therapies that can help.
If you can establish which singly underlying cause or causes are the key issues surrounding your individual child's dyslexic symptom then both you and the school can start to make headway in helping.
My son has receptive language difficulties, but visually he's hawk eyes, so school use a very visual style with lots and lots of visual prompts and aids to help him learn. Another child might have the opposite problem in which case that child would never make progress by being taught using the methods that suit my lad so well. Yet both children are "dyslexic". Lots of time & effort is wasted by many schools through not understanding the underlying causes of an individual child's dyslexia.
If the EP can establish the child's strengths then these can be used as "hook" to help pull up the areas of deficit by skilled educators. This can only be done by administering standard cognitive tests such as WISC. Make sure you get the full unedited scores yourself as these can be very valuable to you for helping you decide what home therapies etc to implement to help your child.