It's the 85th percentile actually. And he is right that the speed survey doesn't apply in a school zone and a fence doesn't invalidate the school zone if you're actually abreast of the school building or property. All that talk of fences applies only to the "approach or passing" (that is, it's area marked as a School Zone that's beyond the school property itself). Where exactly did he observe you speeding? What time of day?

Judicial error isn't going to get you aquitted, just back for another trial.