Engineering drawing is valuable in capturing geometric features, conveying engineering ideas, and creating a blueprint of the intended product. Engineering students usually perform orthographic projections, imagining a 3D situation and sketching its 2D representation. That requires imagination and mental visualization, determined by the learner's spatial ability. This study proposes the infusion of an AR stereogram mobile application into an engineering drawing course to establish how it influences learning outcomes among students with different spatial abilities. The quantitative experimental study involved two mechanical engineering classes in northern Taiwan, N = 69 first-year vocational high schoolers. Statistical analysis revealed that the experimental group with high spatial ability recorded better results and excellent drawing skills. Bloom's taxonomy categorization reported that spatial ability influenced "understanding" and "applying" levels, with the strongest effect on "understanding." Although no significant interaction existed, learning outcomes were highly affected by spatial ability in "understanding" and "applying" levels and AR in the overall performance. The findings and discussions show AR holds great potential to enhance students' spatial ability for real-time visualization and enables better concept comprehension by improving their understanding of engineering topics. Future studies should consider these implications in creating effective and immersive learning environments for different courses in engineering education.