We adapted to Spanish language, from the Diagnostic reading scales, by Spache, the reading passages sequenced by difficulty level from first to eigth grade, that evaluate reading at the instructional, independent and potential level. We applied these passages to a group of 627 Chilean children of both genders, 5, 6 years to 16 years old, from state and private schools. We analyzed results in reading quality, speed, errors and comprehension; comparing achievements between children from both school systems, where significant differences between both groups were found.