Michael and Marla Sklar (plaintiffs) paid tuition for their children’s education at a private religious school. Without explanation or proof, the Sklars claimed that 45 percent of the tuition was for a secular component equivalent to the value of secular education in a public school, and that the other 55 percent was for a religious component. The Sklars claimed a charitable-contribution tax deduction under § 170 of the federal tax code for the religious component of the tuition. The commissioner of internal revenue (commissioner) (defendant) disallowed the deduction. The Sklars filed a petition challenging the disallowance, and the tax court ruled for the commissioner. The Sklars appealed again.