This book addresses the question of what tests are measures of. Intelligence, achievement, and personality tests not based on empirical investigation have questionable validity. Some researchers now suspect that almost all tests given to students in all subjects, as well as general tests of intelligence and personality, are essentially language tests. This book is a first step in the investigation of language proficiency as a factor in educational tests. Five researchers discuss: (1) the importance of language proficiency to IQ and other educational tests (John W. Oller, Jr.); (2) content similarities between intelligence, achievement, personality and language tests (Bjarni Gunnarsson); (3) cloze and dictation tasks as predictors of intelligence and achievement scores (Thomas A. Stump); (4) relationships between oral and written cloze scores and achievement test scores in a bilingual setting (Virginia Streiff); and (5) language proficiency as a source of variance in self-reported effective variables (John W. Oller, Jr. and Kyle Perkins). This book can be used in courses on counseling and guidance, educational measurement, the psychology of language, educational linguistics, and language testing. It also has relevance to the problems of bilingual/bicultural education and multilingualism. Tests cited and references are appended. (Author/NCR)