The purpose of this study is to determine the impact of heuristic strategy on students' mathematical abilities in high order thinking. This descriptive research uses a correlation design. The population of this study were all second-grade public and private high school students representing schools from eight districts in North Sumatra province, and samples (N = 257) were taken randomly. Based on linear regression analysis through analysis of variance (ANOVA) results obtained that heuristic

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... tegy has a very strong influence on students 'mathematical abilities in high order thinking, and partially heuristic strategies affect students' ability in (1) understanding of concepts, (2) creativity, (3) mathematical communication, (4) problem solving, and (5) reasoning ability.