Which type of reading assessment provides information about students' prior knowledge and skills?

The choice of diagnostic assessment is indeed the right answer because this type of assessment serves the purpose of evaluating a student's existing knowledge, skills, and understandings before instruction takes place. It aims to identify strengths and weaknesses in reading abilities, which allows educators to tailor instruction to meet individual needs. By assessing prior knowledge, diagnostic assessments help teachers to plan effective lessons and interventions based on the specific requirements of each student.

Formative assessments, while also important, are primarily used to monitor student learning progress during instruction and provide ongoing feedback to improve teaching and learning. Summative assessments typically occur at the end of a unit or course to evaluate overall student learning through a cumulative measure, rather than focusing on prior knowledge. An informal reading inventory, although helpful in assessing reading levels, is often more about evaluating current reading performance rather than specifically diagnosing prior knowledge and skills.