The assessment and diagnosis of learning disabilities (LD) in the school is problematic. How do educators determine who is learning disabled? What practices are recommended? The main focus of the paper is on specific, relatively technical points that influence the validity of assessment. Since technical concerns are only one of the factors influencing the validity of placements, this paper is organized into two sections: the context of LD identification and technical issues in LD assessment. Specific propositions regarding the context of LD identification are advanced with supporting evidence: overidentification in the LD category; ambiguity in the definition of LD and local idiosyncratic criteria; students' needs for special help; parental demand and pressure from regular education; teaching and system failures; and the consequences of overidentification. Technical topics related to steps in the assessment process are referral bias; normal variability and clinicians' vertigo; technical adequacy of tests; specialists' knowledge of test adequacy and measurement concepts; significant ability-achievement discrepancy; interpreting subtest scatter; using age norms to evaluate processing deficits; behavorial indicators, informal assessments, and clinical hypothesis testing; and exclusion and bias. Recommendations made include contextual changes that are likely to help clinicians be willing to make more rigorous diagnoses and improved training and retraining of specialists. (PN)