[4] Dyslexia is separate from reading difficulties caused by hearing or vision problems or by insufficient teaching or opportunity to learn.

People with acquired dyslexia exhibit some of the signs or symptoms of the developmental disorder, but require different assessment strategies and treatment approaches.

[18] In early childhood, symptoms that correlate with a later diagnosis of dyslexia include delayed onset of speech and a lack of phonological awareness.

[10] A common myth closely associates dyslexia with mirror writing and reading letters or words backwards.

[10] School-age children with dyslexia may exhibit signs of difficulty in identifying or generating rhyming words, or counting the number of syllables in words—both of which depend on phonological awareness.

[22]: 647  People with dyslexia are commonly poor spellers, a feature sometimes called dysorthographia or dysgraphia, which depends on the skill of orthographic coding.

[10] Problems persist into adolescence and adulthood and may include difficulties with summarizing stories, memorization, reading aloud, or learning foreign languages.

[35][36] For example, some have tried to associate the common problem among people with dyslexia of not being able to see letters clearly to abnormal development of their visual nerve cells.

fMRIs of people with dyslexia indicate an interactive role of the cerebellum and cerebral cortex as well as other brain structures in reading.

[42] The fact that some children with dyslexia have motor task and balance impairments could be consistent with a cerebellar role in their reading difficulties.

[37] Observed anatomical differences in the language centers of such brains include microscopic cortical malformations known as ectopias, and more rarely, vascular micro-malformations, and microgyrus—a smaller than usual size for the gyrus.

Abnormal cell formations in people with dyslexia have also been reported in non-language cerebral and subcortical brain structures.

[55]: 266  English and French have comparatively "deep" phonemic orthographies within the Latin alphabet writing system, with complex structures employing spelling patterns on several levels: letter-sound correspondence, syllables, and morphemes.

[56]: 421  Languages such as Spanish, Italian and Finnish primarily employ letter-sound correspondence—so-called "shallow" orthographies—which makes them easier to learn for people with dyslexia.

[55]: 266  Logographic writing systems, such as Chinese characters, have extensive symbol use; and these also pose problems for dyslexic learners.

In other studies, dyslexia is correlated with anatomical differences in the corpus callosum, the bundle of nerve fibers that connects the left and right hemispheres.

[58] Data via diffusion tensor MRI indicate changes in connectivity or in gray matter density in areas related to reading and language.

Finally, the left inferior frontal gyrus has shown differences in phonological processing in people with dyslexia.

[58] Neurophysiological and imaging procedures are being used to ascertain phenotypic characteristics in people with dyslexia, thus identifying the effects of dyslexia-related genes.

[61] One mechanism is the lexical route, which is the process whereby skilled readers can recognize known words by sight alone, through a "dictionary" lookup procedure.

[55][64] Dyslexia is a heterogeneous, dimensional learning disorder that impairs accurate and fluent word reading and spelling.

[72] The National Institute of Neurological Disorders and Stroke describes dyslexia as "difficulty with phonological processing (the manipulation of sounds), spelling, and/or rapid visual-verbal responding".

[73] Phonological awareness enables one to identify, discriminate, remember (working memory), and mentally manipulate the sound structures of language—phonemes, onsite-rime segments, syllables, and words.

Careful observation of the child in the school and home environments, and sensitive, comprehensive parental interviews are just as important as tests.

These tests and observations can include:[86] Screening procedures seek to identify children who show signs of possible dyslexia.

[105] There is currently no evidence showing that music education significantly improves the reading skills of adolescents with dyslexia.

[115][116][117] He used the term to refer to the case of a young boy who had severe difficulty learning to read and write, despite showing typical intelligence and physical abilities in all other respects.

[119] The distinction between phonological versus surface types of dyslexia is only descriptive, and without any etiological assumption as to the underlying brain mechanisms.

[122] If the instructors of a person with dyslexia lack the necessary training to support a child with the condition, there is often a negative effect on the student's learning participation.