The purpose of the study is to explore whether first-year university students' performance in an argumentative writing test is related to their performance in tests of inference analysis, argument analysis and syllogistic reasoning as well as their academic achievement, as measured by their previous high school grades and by two standardized tests required for university admission in Chile. 452 first-year undergraduates participated in the study. The results show that the information originated from the writing and thinking assessments supplements the information provided by the academic measures. The inference and argument analysis tests did not replicate the achievement gap between public, voucher and private schools commonly observed in Chile. The results showed that gender differences in writing are relatively independent of gender differences in thinking. The results support the adoption of writing and thinking measures as a part of initiatives targeting the identification of abilities not tested by conventional academic assessment.