I think I might approach this differently.

How about asking what happened in class that he didn't learn a thing, as illustrated by the DRA? Your child is entitled to one full year's growth each year, and this DRA score shows he didn't grow, and in fact declined based on his percentile rank.

http://www.wrightslaw.com/advoc/articles/tests_measurements.html#progress

Look down to "When apparent progress means regression"

I think you have a case that his teacher has been a disaster this year, and that the school needs to do some remediation to get him back up to where he was at the beginning of the year.