Abstract: Ten-structured thinking is a major conceptual advancement in the primary mathematics classroom. This study involves the assessment of ten-structured thinking of 108 Grade 2, 80 Grade 3, 109 (35 Honors and 74 Non-Honors) Grade 4, and 142 (33 Honors and 109 Non-Honors) Grade 5 pupils of the Ateneo de Davao Grade School. The pupils were asked to solve a range of written assessment tasks that focus on ten-structured thinking. Tasks include subitizing, grouping by tens, incrementing or decrementing by tens or ones, and adding and subtracting numbers. Results indicate relative difficulties with certain number patterns, with non-canonical number representations, and with bridging through tens or hundreds. Further, pupils from Honors sections significantly outperformed those from non-Honors sections, and the gap is more evident in the more difficult tasks. In several tasks, pupils from the Grade 4 Honors section performed as well as those from the Grade 5 Non-Honors sections. Given that the tasks focused on children’s conceptions of number, results from this study suggest a need to construct an environment where the Ateneo de Davao Grade School pupils can be aware of number magnitudes.