WASHINGTON (AP) -- Many fewer disabled children take the nation's reading and math tests than the government has previously said, congressional investigators acknowledge.The Government Accountability Office reported in July that only 5 percent of students with disabilities are excluded from the National Assessment of Educational Progress.Now the GAO says that figure is eight times higher. For example, 40 percent of fourth-graders with disabilities who were in the sample for the 2002 reading test didn't take it.The discrepancy is important because the federal test, known as the Nation's Report Card, is supposed to be representative of all students, including those with disabilities. The higher the rate of exclusions, the more some students' scores and needs may be left behind.The mistake resulted from miscommunication between the GAO, which is the auditing arm of Congress, and the Education Department, which provided the data on the disabled students.Typically, students are excluded from the testing because, unlike many state tests, the federal exams cannot accommodate some special needs. For instance, passages cannot be read aloud to students because the reading test measures a student's ability to read the written word.Advocates for disabled children say that although some students cannot take the federal test, the GAO's revised number of excluded kids, 4 in 10 children, was alarming."It denies the country an accurate picture of how students are performing on the most important tracking assessment that we have," said James Wendorf, executive director of the National Center for Learning Disabilities. "Kids with disabilities deserve to be included."In a letter Monday to Sen. Edward Kennedy, the Massachusetts Democrat who requested the initial report, the GAO said the exclusion rates are "much higher than previously reported."The 5 percent figure the GAO originally used reflects the number of students with disabilities who were excluded from testing when compared with the entire sample of students.Yet when the number of disabled children who were kept out of testing is compared only with the sample of students identified with disabilities, the exclusion rates are much higher.The GAO said the Education Department only pointed this out in September, more than two months after education officials examined the draft report and raised no questions about its accuracy. The GAO routinely gives agencies a chance to comment before releasing reports.But Education Department officials say they have been consistently reporting the exclusion rates for years and are not to blame for how the numbers were misinterpreted."GAO made a mistake in their report and we didn't catch it," said Russ Whitehurst, director of the Institute of Education Sciences, an arm of the Education Department. "As soon as we found out about it, we alerted them that there had been a problem."The independent board that oversees the federal tests is working on uniform ways to help more disabled children participate in the tests.The percentage of disabled students who were excluded has been declining -- from 57 percent in 1992 to 40 percent in 2002 to 35 percent in 2005 in fourth-grade reading. The numbers are better in math. In fourth-grade math, 19 percent of students with disabilities were excluded from the test in 2005, down from 26 percent five years earlier.The bigger worry, Whitehurst said, is when states have widely different accommodations for students with disabilities. Such variation leads to some states excluding few students and some excluding many, which erodes the value of the test as measuring stick across states.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.