Changing the angle of rotation

What is the most important skill for students to have in their robot building?

I've thought about this a lot recently and everything is so intertwined that to pin point a single skill is proving difficult. Students need to have the ability to make a strong model, using a minimal quantity of but also the appropriate pieces. Students need to have the understanding of some simple machines concepts like gears and leverage, not only how the concepts work but how they can implement them in their creations.

So what's the answer?  Firstly I think the more students build the better they become, they see which pieces work together and which ones don't.  The better they know the pieces the better they can become working with them and knowing which piece is the most appropriate.   To practice this I've recently been asking students to come up with multiple ways of 'changing the angle of rotation'.  Meaning, connect two gears so that the drive gear is turning on the x axis or horizontally (blue) and the driven gear is on the y axis/vertically (tan).

I find this is a really tricky task for many students. While they easily get the concept they often struggle actually connecting the two and come up with convoluted systems of axles and bent liftarms to achieve something that partly resembles the brief.

That's where these pieces come in handy, each of these pieces change the direction of the technic beams and provide some clues for students.  I'm still finding I need to show them some models either physically or from one of Yoshihito Isogawa's books to help them see how the pieces work but with this help they are starting to improve their knowledge of technic engineering, becoming more confident with the pieces and are increasingly solving more challenges.