Caveat Lector! This potential drop in percentage is not due to a cataclysmic failure of New Jersey's public schools, but rather a change in the graduation-rate percentage formula! The data will be EXTREMELY misleading to the average reader.
Why is New Jersey's formula changing? Outside of the fact that this is a Federal requirement for next year, the data would provide an equal, state-by-state comparison for grade-rate calculations. The new formula uses an adjusted cohort graduation calculation called a Cumulative Promotion Index (CPI). Previously, states, similar to New Jersey, self-reported the data. New Jersey used its own formula for this calculation.
What is New Jersey's new formula? According to NJ Spotlight, the CPI tracks "the students who enrolled as freshman through their graduation to determine actual graduation rates." In New Jersey, this "tracking" will occur through NJ SMART system. Additional information regarding NJ SMART can be found at http://www.nj.gov/education/njsmart/.