In a report issued Tuesday, Superior Court Judge Peter Doyne found that Christie's cuts hit high-risk districts the hardest.
The state Supreme Court will now consider his finding and whether to act on it.
The Supreme Court has ruled repeatedly that the state needs to do more to improve schools in New Jersey's poorest districts.
Last year, Christie cut state funding for all districts, including the needy ones, saying the state government couldn't balance its budget otherwise.
An education advocacy group sued, saying the cuts deprived students of the quality education mandated by the state constitution.