Elena Kagan the U.S. Supreme Court justice donned her hat as Kagan the law teacher on June 9 as she sorted out the meaning of one of the densest statutory schemes the court has had to rule on in years.

Her opinion in Scialabba v. Cuellar de Osorio dealt with visa eligibility of immigrants’ children when they “age out” and turn 21 while their applications are pending. Kagan adopted the Obama administration’s narrow reading that the law means most applicants will have to go to the “back of the line” when they turn 21, adding years of delay. The ­different categories to which certain relatives of immigrants are assigned under federal regulations were key to the decision.