Last year, the school of my then-P.1 kid adopted "Reading A-Z" program. According to the correlation table (http://www.readinga-z.com/correlation-chart.php), my kid had read up to Level 1X last year.
However, a high level does not mean one can comprehend what is being read completely. After all, if a kid knows basic phonics skills, he or she can read multi-syllable words without understanding their meanings.