Based on a review of standardized tests and competency assessment instruments, recommendations are made for identifying and selecting standardized tests to help secondary vocational instructors to develop students' basic skills. Chapter 1 focuses on identifying diagnostic tests of basic skills in reading, mathematics, and communication. It discusses the concept of diagnosis and criteria for selecting tests. Four types of diagnostic tests are described: (criterion-referenced, norm-referenced, custom-made or made-to-order, objectives-based item banks), and suitable tests of each type are named. How diagnostic testing will be presented in the Resource and Teacher Guides of the project, Teaching Basic Skills Through Vocational Education, is considered. Chapter 2 focuses on competency instruments to assess students' basic skills. It reviews requirements faced by students for proficiency in basic skills and then discusses each set of requirements in terms of the competency instruments recommended for its assessment. Recommendations are made for inclusion of assessment instruments in the Guides. Appendixes include a list of norm-referenced tests that were screened out, format for test review, list of tests on basic skills that have vocationally relevant testing materials built in, and references related to readability analysis. (YLB)