An essential difficulty in solving practical problems that are not like the ones a student has solved before is discerning the core of the problem. It is claimed that discernment has to be trained by variation--by varying the context of the assignments in which students have to identify and grasp their "underlying form". A decisive challenge in engineering education--and also medicine, veterinary and pharmacy--is that there are many and very different kinds of subjects students study, some with thoroughly scientific content, others centred on more practical knowledge. How to provide a coherent program keyed on discernment? Another challenge is what's required to apply theory to practice; i.e. theory needs to be restructured and often integrated with parts of other theories and with more practical knowledge before it can be applied in real-life problem solving. What we propose is to let the variation of assignments transcend subject borders. Give assignments in the same subject that vary in context, e.g. from theoretical and "closed" to practical and "open". And give assignments in different subjects embodying the same concept, principle or method, thus training discernment and at the same time demonstrating relations between theoretical and more practical subjects. (Contains 2 figures.)