A study conducted in four Wisconsin secondary schools attempted to measure student abilities in evaluating verbal argument and to determine the grade level at which verbal argument concepts and skills should be appropriately taught. Seven tests, known as the Wisconsin Tests of Testimony and Reasoning Assessment (WISTTRA), were administered to 3000 students in grades 7-12; three of the tests measured the ability to detect testimony violating common internal and external tests, and four tests measured the ability to recognize and question essential parts of an argument and to draw appropriate conclusions from it. Data indicated that (1) since the greatest change in mean scores between adjacent grades occurred between grades 9 and 10, grade 10 may be the optimum time to teach these abilities, (2) females seem to acquire these critical abilities earlier than do males, and (3) student scores on verbal argument correlated only low to moderate with their scores on intelligence and reading tests. (Included are charts which correlate test data at each grade level.) (See also ED 036 521, TE 001 784, and ED 016 658.) (JB)