A persistent problem in engineering-focused science instruction is the "design--science gap," whereby learners focus on building successful engineering products, instead of focusing on the relevant scientific principles. This research explores (a) whether integrating contrasting cases into engineering activities can impact how deeply learners notice scientific structures both within the engineering task and in novel transfer contexts, and (b) whether the perceptual process of "noticing" is related to task performance and transfer. In Study 1, 41 adults designed and built a Lego cantilever, which relates to the physics concept center-of-mass. Learners who analyzed "contrasting cases" that highlighted the underlying structure of center-of-mass noticed that structure more deeply, compared with a "no cases" condition. Although both conditions performed similarly on the engineering task, learners who noticed on a deeper level performed better, regardless of condition. In a second study with 63 adults, the same two conditions were compared with a "single cases" condition. The "contrasting cases" condition demonstrated superior transfer to near but novel contexts. Moreover, noticing predicted performance and far transfer, regardless of condition. Results imply that (a) contrasting cases enhance near transfer from engineering activities and (b) noticing plays a key role in performance in and transfer from engineering activities.