The DRA is somewhat subjective because the child has to answer questions that the teacher might not think are complete enough. There is a writing portion once you get past a certain level, and kids who don't like to write might not writie enough. Also, the child must read aloud a portion of the text. Shyness and learning disabilities could figure in there. If you know a teacher who uses the DRA (sometimes teachers tutor if you don't have a personal friend), he or she might test your child. Also, the DRA scores include how fast a child reads. Kids with slow processing (some kids just do everything slow) and kids from the deep south don't always read fast enough.
One of my dc was testing at grade level in 5th grade, but his Lexile score was at a post-secondary level. What that means is he could read and comprehend on a higher level than he was willing/able to write about.