Teachers are often perplexed realizing students ending up with different understandings of the same lesson after attending the same class. This study investigates the use of Variation Theory as a pedagogical design tool in improving students' problem-solving skills in trigonometry. This action research utilizing the 'Learning Study' approach was conducted in a Filipino-Chinese private school in a highly urbanized city in the Philippines. Two Grade 10 intact classes consisting of a total of 41 students and three mathematics teachers participated in the learning study. Selected students were interviewed to validate students' intended and lived objects of learning. The video-recorded lessons were examined to determine the alignment of the intended and enacted objects of learning. The analysis of the pretest and posttest showed the use of different patterns of variation and invariance in teaching was able to address students' misconceptions and difficulties in solving right triangles and helped the students understand problems better. Thus, the Variation Theory of learning as a pedagogical design tool is deemed effective in improving the students' knowledge, procedural, and problem-solving skills, and in bridging the gap between the intended objects of learning and the lived objects of learning.