Unschoolers knew this well. :-)
For those who only believe "scientific proof," though, here it is:
A University of Otago researcher has uncovered for the first time quantitative evidence that teaching children to read from age five is not likely to make that child any more successful at reading than a child who learns reading later, from age seven.
The ground-breaking Psychology PhD research, conducted by Dr Sebastian Suggate, has been placed on the University's "distinguished list" of doctoral theses for 2009. Dr Suggate has also been awarded a prestigious Postdoctoral Research Fellowship from the Humboldt Association in Germany to the University of Wuerzburg in Bavaria to further his studies into childhood education.
Starting in 2007, Dr Suggate conducted one international and two New Zealand studies, each one backing up the conclusions of the other; that there is no difference between the reading ability of early (from age five) and late (from age seven) readers by the time those children reach their last year at Primary School by age 11.
Comparing children from Rudolf Steiner schools, who usually start learning to read from age seven, and children in state-run schools, who start learning to read at five, he found that the later learners caught up and matched the reading abilities of their earlier-reading counterparts by the time they were 11, or by Year 7.
read the rest: http://www.voxy.co.nz/national/research-finds-no-advantage-learning-read-age-five/5/33888