That's a big difference between the two most populous states in the country.
What are the reasons?
P.S., Your Lying Eyes has a good post, Achievement Gap Grows with Achievement, on how the white-black gaps within states tend to get larger the higher the white scores. Thus, New Jersey has the highest white reading score and the largest white-black gap.
Two states that stand out are Wisconsin, where blacks just do badly without whites doing particularly well, and Texas, where, at least on math, whites score well but the white-black is only middling due to blacks doing relatively well. (Hispanics also score well on math in Texas. Does Texas just bribe kids into trying really hard on the NAEP, or are they actually doing something right with teaching math in Texas?)