The National Association for College Admission Counseling does not recommend spending much on SAT prep classes.
Its research suggests that increased scores aren't "that much greater than what you could get on your own with practice tests," said research director David Hawkins.
The group's report last month on standardized tests said most prep programs result in a 20- to 30-point gain.
Larger increases could be due to such factors as familiarity with the test, more time in school or simple maturity, said Derek Briggs, a test expert at the University of Colorado.