Examines U.S. and Chinese 6th grade students' mathematical thinking and reasoning involved in solving six process-constrained and six process-open problems. Concludes that the Chinese sample had a significantly higher mean score than the U.S. sample on the process-constrained tasks, but the sample of U.S. students had a significantly higher mean score than the Chinese students on the process-open tasks. (Contains 43 references.) (Author/ASK)