Which aspect is crucial for the educational diagnostician when determining eligibility for special education services?

Determining eligibility for special education services heavily relies on achievement test scores and intelligence testing because these assessments provide quantitative data that help in assessing a student's academic functioning and cognitive abilities. This information is vital as it allows the educational diagnostician to make informed comparisons between a student's performance and the expected developmental milestones for their age or grade level.

Achievement test scores reflect what a student has learned in specific subject areas, while intelligence tests measure general cognitive ability, which can reveal whether a student's academic challenges are due to a learning disability or another factor. Together, these scores help form a comprehensive understanding of the student's educational needs and are critical in developing tailored interventions.

While parental input, classroom behavior, and previous school reports can offer valuable context and insights into a student's educational experience, they are typically not sufficient on their own to determine eligibility. Test scores provide objective criteria that support the decision-making process in a standardized way, ensuring that the evaluation is based on measurable data.