Here is a link to a publication from NCWD-Youth (Joan Wills and Curtis Richards) on assessments for youth with disabilities. It is probably the best resource for work-based assessments. The guide is free to download.
http://www.ncwd-youth.info/resources_&_Publications/assessment.html
Theda Nixon
INSOURCE Program Specialist
1703 S. Ironwood Drive
South Bend, IN 46613
1-800-332-4433
574-234-7101
574-234-7279 (fax)
tnixon@insource.org