Creating an environment where challenge exceeds skill essentially means creating an environment in which there is a high degree of rigor. Many people think they understand the meaning of rigor, but it turns out their understanding is way off. Rigor is not about repetition. In a highly effective classroom, rigor is about challenging students beyond where their existing skills are at. By doing so, you create a gap between where they're at and the skills that they need to accomplish something in a certain task or challenge. That gap is the opportunity for growth.
For instance, if all you do is give students words that they already know, they don't develop new vocabulary. In order to teach them new vocabulary, you need to offer those words to them and then give them a setting in which to absorb these terms through personal engagement with them. (Note that this is not the same as expecting rote recall of definitions.) That’s a simple example, but demonstrates what it means to create a rigorous environment: putting students in a situation that encourages them in the acquisition of new knowledge and skills.
If all you do is give students what to do, they don't ever develop the skill needed to plan what to do. They don't learn how to develop models; they only learn how to use models. This is not only connected to standards and STEM subjects.
ELA and math both get a lot of use during STEM time on learning. The intersection of all three skill areas requires those higher order thinking skills of creating, analyzing and evaluating. In fact, true inquiry requires such a high degree of ELA and math that you could actually call some of the time spent on science and engineering math or ELA time.
Creating an environment where challenge exceeds skill is not just unique to science or engineering. In fact, it uses ELA and math as part of that science and engineering time. You could even make an argument that it wouldn’t even be necessary to label the time you spend on STEM subjects as such, but to just apply that time on learning to math or to ELA. Creating an environment where challenge exceeds skill means engaging in answering questions and solving problems as scientist and engineers do. Challenging students to do that by creating concept to concept, concept to self, and concept to world connections inevitably requires leveraging their ELA and math skills. These in turn help them perform in three dimensions.