Formative assessment takes place during a unit or a course, module, with a focus on gathering data about students' progress to help them improve language skills and fill in communicative gaps. It is essential for all students to have access to the general curriculum, including reading and math instruction. Students with cognitive disabilities may require effective instruction to achieve alternate achievement standards for reading or math. Subjective assessment involves the assessor's impression or opinion contributing to the evaluation of performance. Facility value is a statistical measure of test item difficulty.