bad reporting or bad research?

I heard a report on TV news this morning that said that children who are held back and start school a year later than is typical don't do better in school (which has long been the assumption).  Since my son was "held back" a year (back then they had an extra year built in called "Reading Readiness") and has subsequently done very well, this comment caught my attention.  The reporter said when 8 year olds who started school later are tested against 8 year olds who started on the usual schedule they don'd do as well on standardized tests.  Well, do you think that could possibly have something to do with the fact that the late starters have one less year of school under their belts?  How about testing 2nd graders against other 2nd graders, or 8th graders against 8th graders, and then comparing the early starters to the late?