The paper reviews findings and implications of curriculum based assessment (CBA), an approach focusing on collecting, interpreting, and using data to help lower achieving students have opportunities for success in mainstreamed settings. An instructional delivery model is presented to guage the probability of task success and provide a structure for controlling the difficulties encountered by a teacher in deciding what and how to teach. Three performance levels of student functioning are proposed: frustrational level, instructional level, and independent level. Percentages of challenge provided for the instructional level constitute a manageable set of criteria to evaluate the suitability of students' assessment. Studies are cited to illustrate the use of the model with attention deficit disordered and low achieving students. (CL)