According to Koelsch, Estrin, and Farr (1995) "an important principle of assessment equity states that a more valid picture of what a student has learned and can do is likely to emerge when multiple sources of information are used." English learners do not always have the schema, vocabulary, and cultural connections necessary to perform well in assessments. For this reason, basing decisions on a sole assessment or one type of assessment should not be the sole measure of a student's achievement or learning, particularly when that assessment uses language in which the student is not yet proficient.
What is the difference in using diagnostic, formative and summative assessments for monitoring English Language Learners' progress/performance? Provide two purposes for each assessment.
Traditionally,a diagnostic assessment is given at the beginning of a learning cycle or unit. It help the teacher determine what the student(s) may already know as contrasted with what it is that you want them to know. This provides the foundation upon which to base your instructional strategies. Here is a relevant link for using diagnostic assessment as a tool to establish a baseline for developing oral proficiency:
2. A formative assessment is ...
This job shows the difference in using diagnostic, formative and summative assessments.