Complex sentence: The objective, according to the the NYC DOE, was to combat the advantages of children receiving pretest tutoring--the OLSAT is more preppable, the NNAT is less preppable.
Split into simpler sentences: The objective, according to the the NYC DOE, was to combat the advantages of children receiving pretest tutoring. The NYC DOE avers that the OLSAT is more preppable and the NNAT is less preppable.