Minnesota provides its citizens with free elementary and secondary schooling. Approximately 91,000 elementary and secondary students attended some 500 privately supported schools located in Minnesota, and about 95% of these students attended schools considering themselves to be sectarian. Minnesota permits state taxpayers to claim a deduction from gross income for certain expenses incurred in educating their children. The deduction is limited to actual expenses incurred for the 'tuition, textbooks and transportation' of dependents attending elementary or secondary schools. A deduction may not exceed $500 per dependent in grades K through 6 and $700 per dependent in grades 7 through 12. P sued claiming that these deductions violated the Establishment Clause by providing financial assistance to sectarian institutions. They named as defendants, the Commissioner of the Department of Revenue of Minnesota and several parents who took advantage of the tax deduction, Allen (Ds). The District Court granted Ds' motion for summary judgment, holding that the statute was 'neutral on its face and in its application and does not have a primary effect of either advancing or inhibiting religion.' The Court of Appeals affirmed. The Supreme Court granted certiorari.