Check the website of the school in question to see if it mentions accreditation. If it does, check the website of the accrediting agency to see if the school is in good standing.
If the school's website does not mention accreditation, check for its name on the website of the accrediting agency that covers the school's area. The six regional accreditation agencies in the United States are the New England Association of Schools and Colleges, Western Association of Schools and Colleges, Northwestern Association of Schools and Colleges, Southern Association of Colleges and Schools, Middle States Association of Colleges and Schools and North Central Association of Colleges and Schools.
Assume the school is not accredited if it is not listed on the appropriate accrediting agency's website.
Follow up with a call to the school's registrar to verify the lack of accreditation.
Remember that regional accreditation means the entire institution is accredited. Several national agencies offer accreditation for certain professional schools and college programs, but this accreditation is narrow in scope and applies only to the school or program in question.