What rationale does the U.S. Supreme Court provide in San Antonio v. Rodriguez with regard to school finance that would justify one town in the state of New Jersey spending $14,000 per pupil, while another town chooses to spend $21,000 per pupil?

What rationale does the U.S. Supreme Court provide in San Antonio v. Rodriguez with regard to school finance that would justify one town in the state of New Jersey spending $14,000 per pupil, while another town chooses to spend $21,000 per pupil? Even though not illegal, do you find the differences in district spending unethical? Why or why not?