A juvenile offender’s prison sentence that is so long it may as well be a life term violates the Eighth Amendment, the U.S. Court of Appeals for the Third Circuit held April 9.

It was an issue of first impression for the circuit court.

Most other circuits reached the same conclusion, it said. The Eighth Circuit is the outlier.

Corey Grant’s crimes reflected “transient immaturity” rather than “irreparable corruption,” Judge Joseph A. Greenaway Jr. wrote for the Third Circuit.

Grant...