Here is an article published by the University of Cambridge which discusses the advantages of starting formal schooling later and delaying literacy lessons until the age of 7. We tend to agree and that is why our preschool programs include children age 5 and 6.
Studies have compared groups of children in New Zealand who started formal literacy lessons at ages 5 and 7. Their results show that the early introduction of formal learning approaches to literacy does not improve children’s reading development, and may be damaging. By the age of 11 there was no difference in reading ability level between the two groups, but the children who started at 5 developed less positive attitudes to reading, and showed poorer text comprehension than those children who had started later. In a separate study of reading achievement in 15 year olds across 55 countries, researchers showed that there was no significant association between reading achievement and school entry age.