Intended for classroom teachers who have English Language Learners (ELLs--non-native speakers of English who are experiencing difficulty in learning academic content), this guidebook provides criteria to be included in the development of performance-based assessment tasks. It assists classroom teachers to develop assessments to: determine whether a student may be an ELL; measure native language proficiency and/or English language proficiency; determine initial instructional placement for an ELL in mathematics and/or reading; measure the academic achievement of an ELL in mathematics and/or reading in their native language and/or in the English language; and provide information on the development of databases to be used in monitoring student performance on the assessments administered. After an introduction, sections of the guidebook are: (1) List of School Reform Initiatives for Teachers of English Language Learners (ELLs); (2) Discussion of Performance and Content Standards for Teachers of English Language Learners; (3) General Guidelines To Be Aware of When Assessing English Language Learners; (4) Assessment Accommodations for English Language Learners; (5) Development of Assessment Instruments to Identify English Language Learners; (6) Development of Assessment Instruments To Measure English Language Learners' Native Language and English Language Proficiency; (7) Development of Assessment Instruments for Initial Instructional Placement of English Language Learners in Mathematics and Reading; (8) Development of Assessment Instruments To Measure Academic Achievement of English Language Learners in Mathematics and Reading; and (9) Development of Databases in Evaluation of English Language Learners Programs. Addresses of 15 Comprehensive Regional Assistance Centers and a 53-item bibliography are attached; appendixes contain "A Reader's Own Scoring Guide," the Six-Trait Analytical Writing Assessment Model, and "E.A.R.--Conceptual Framework for the Traits of Competent Oral Communication." (RS)