Statements that describe what students should know or be able to do at the end of a period of study are best described as:

The description of what students should know or be able to do at the end of a period of study aligns perfectly with the concept of standards. Standards provide clear expectations and benchmarks for learning outcomes in education, serving as guides for both educators and students. They outline the knowledge, skills, and competencies that students are expected to achieve and can cover various subjects and grade levels.

Standards also help educators design curriculum and assessments that align with specific learning goals, ensuring consistency in what is taught and assessed across different classrooms and schools. By focusing on these defined standards, educators can effectively measure student progress and direct their instruction to meet these established educational benchmarks.

Assessments, on the other hand, are tools used to evaluate student learning in relation to the standards but do not define what those standards are. Performances refer to the actual demonstration of skills or knowledge, and rubrics are specific criteria used to evaluate those performances. Thus, while these concepts are related to the overall educational process, they do not encapsulate the idea of defining expected knowledge and skills at the end of study periods like standards do.