Yes. As part of psychological assessments for children with suspected learning problems, there are formal tests of reading ability that can be done. School psychologis can perform these tests. Added to these are tests that can be done by speech and language therapists.
Special testing. Dyslexia is a learning disability and many schools will offer educational testing which can diagnose the learning deficiencies including dyslexia. If the school won't do it there are educational specialists ( usually pschologists or phd's) who are very capable of testing and directing you for help.
A language-based . learning disability, dyslexia is caused by the brain's inability to process phonemes, the smallest units of sound in a language. Risk factors are + family history, early language delays, difficulty in sound-symbol association (like p-puh) & in rhyming. 70% of Neurotypical (NT) 5-yr-olds & 100 % of NT 6-yr-olds have phonological awareness & know how many sounds are in the words "cat", "boat", etc.