The Supreme Court held unanimously last week — in its most momentous ruling on special education in over three decades — that the standard for services owed to students with disabilities under federal law is higher than “merely more than de minimis.”

Lower courts had been divided, with some saying services must be “meaningful” or “significant,” and others saying “merely more than de minimis” — as in a step above trivial.

The Supreme Court decision to raise the bar was generally hailed as a victory for students with disabilities. But don’t believe it. Under the de minimis standard, there was almost nowhere to go but up, and the court went up only a very little. An 8-0 vote by a court that is usually sharply divided is a sign that the decision may lack clarity or bite.

Chief Justice John G. Roberts Jr., writing for the court, stated that the standard is whether the services are “reasonably calculated to enable a child to make progress appropriate in light of the child’s circumstances.” That means more than de minimis, but how much more? The vague language was deliberate to allow, Chief Justice Roberts reasoned, “deference” to the expertise and judgment of school authorities.

But this reasoning is deeply flawed. The court does not understand the extent to which school systems nationwide fail to recognize that the great majority of students with disabilities are capable of achieving much higher levels of academic achievement than they do.

Low expectations are at the root of the failures of special education. Former U.S. Secretary of Education Arne Duncan concluded: “No belief is more damaging in education than the misperception that children with disabilities cannot really and shouldn’t be challenged to reach the same high standards as all children.”

Federal regulations specify that students who are not significantly cognitively disabled should receive services that enable them to meet state standards. This regulatory standard is based on research. The National Center on Educational Outcomes, the leading research organization on accountability for the achievement of students with disabilities has determined that “the vast majority of special education students (80-85 percent) can meet the same achievement standards as other students if they are given specially designed instruction, appropriate access, supports and accommodations as required [by federal law].”

Most educators don’t get it, and the Supreme Court didn’t either. The court decision did not preclude schools from providing services reasonably calculated to enable students to meet grade-level standards. But it simply left them too much room to continue their low expectations and lack of appropriate services.

It is now up to parents and advocates to pressure school systems to raise their expertise and judgment about the potential of students in special education. The expertise must particularly zero in on how to better teach reading. About 90 percent of all students with disabilities who do not have severe cognitive limitations are found eligible for special education because of big deficiencies in reading.