The central obligation under the Individuals With Disabilities Education Act is to provide each eligible student with a free appropriate public education (FAPE). In "Endrew F. v. Douglas County School District RE-1" (2017), the U.S. Supreme Court revised the prior substantive standard for determining FAPE that the court had developed in "Board of Education v. Rowley" (1982). The "Endrew F." court modified the "Rowley" standard of requiring the individualized education program (IEP) to be reasonably calculated to enable the student to receive educational benefit to requiring a student's IEP to be reasonably calculated to enable the student to "make progress appropriate in light of the student's circumstances." The purpose of this article is to compare what the post-"Endrew F." courts use with what the professional literature recommends as measures of appropriate progress. The results inform special education practitioners about the significant discrepancy between the courts' focus on the "must" of legal requirements and the "should" of professional recommendations. The discussion suggests ways that special education professionals can use their expertise to inform courts and legislatures to narrow this gap for the benefit of more effective progress for students with disabilities.