Diagnostic Assessment (DA) is a crucial approach to evaluating students' knowledge and skills, particularly in the field of Second Language Acquisition (SLA). This approach, along with formative, summative, and benchmark assessments, plays a pivotal role in creating personalized study plans and addressing individual learning gaps. 

In alignment with Vygotsky's Sociocultural Theory, which posits that second language learners gain control over tasks through mediated activities, DA delivers prompt and personalized feedback to every learner through a Diagnostic Profile, highlighting their strengths and areas for improvement in their comprehension of reading and listening passages and grammar.  It provides valuable feedback to tailor learning experiences to their specific needs, fitting well within the Proximal Development (ZPD) theory.

Online Diagnostic Assessment (ODA) is a web-based tool that captures students' written responses using constructed-response type questions. These responses offer insights into how students hypothesize about unfamiliar words. ODA evaluates reading and listening comprehension skills, determining proficiency levels and offering formative feedback for progress. It assesses language abilities within ILR levels 1 to 3, adapting to learners' performance dynamically.

ODA primarily focuses on: comprehension, lexicon, syntax, and discourse. It provides learners with immediate, individualized diagnostic profiles, which are crucial for targeted instruction.

This presentation shows how to effectively integrate the ODA Diagnostic Profile into personalized learning plans. ODA is accessible through its website, offering assessment tools for 22 languages, including Korean, Arabic (MSA and dialects), Chinese, Russian, Persian, Spanish, Tagalog, Brazilian Portuguese, French, Pashto, Urdu, Dari, Hebrew, Somali, Turkish, Serbian Croatian, and English.

Keywords: Diagnostic assessment, education, language learning, second language acquisition, learning plan, learner profile.