Which of the following refers to delays in expressing or understanding spoken language?

The answer is oral language disorders. This term specifically refers to difficulties or delays in both the expressive and receptive aspects of spoken language. Individuals with oral language disorders may struggle to articulate their thoughts clearly or may have trouble understanding what others are saying. This can encompass a range of challenges, from limited vocabulary and poor grammar usage to issues with phonological awareness and sentence structure.

The other options do not convey the same specific meaning. Achievement tests assess a student's knowledge and skills in various subjects but do not specifically focus on language disorders. Diagnosis refers more broadly to the process of identifying a problem or condition, which could include a variety of disorders, not solely those related to oral language. Formal testing is a method of assessment that can involve various types of evaluations, but it doesn’t inherently describe the nature of delays in language. Therefore, oral language disorders is the most accurate choice for describing delays in expressing or understanding spoken language.