Brain imaging research has shown that the percentage of children displaying brain patterns indicative of dyslexia in different countries is similar. However, the percentage of children actually having difficulty in learning to read varies greatly across countries. The reason is a characteristic of languages known as transparency.

Transparency refers to the degree to which the orthography (word spelling) of a language directly corresponds to the phonology (word sound) of the language. Finnish and Italian, for example, are very transparent languages. There is a near perfect match between the spelling of a word and the sound of a word in those languages. English, in contrast, is the least transparent language of those languages that have been studied. For example, there are no words like iron and was in the Finnish language. As an aside, in the author’s (James Royer) work with dyslexic children he found that was was misidentified more frequently that any other word. This is partly a function of the frequency of the word in written language, but also a function of the fact that there is no way the word can be identified by sounding out the letters.

Transparency has an enormous impact on learning to read. In Finland 45% of children enter school at age 7 as competent readers and nearly all children are good readers by the end of grade 1. In contrast, 20 percent of children in the U.S. entering grade 1 are at risk for reading failure and many are still not competent at the end of grade 3. In short, it takes an average English reader three years of schooling to reach a level of reading competence attained by nearly all Finish readers in a single year.

Language transparency also makes it much more difficult for a dyslexic child to learn to read. The very large number of irregular words in English (words where spelling and sound do not correspond) means that these words must be memorized, placing an added burden on the dyslexic child. Transparency also has an impact on reading instruction. For example, the teaching of phonics, the process of sounding out words, is more difficult in languages that are not perfectly transparent.