Changing the script
It would be easy to buy some new furniture and create a look of a modern learning environment and then change not much in the way of teaching.
The teacher of the 21st century would need to rethink all they have observed and been of in their teaching so far. Challenges would include the structure of the day - what would a day look like in my class? when would we do things and why? What will I assess and why? What is the nature of the relationships I have with my students? How do I increase the learning capacity of the students in my class? What habits might my students need to "unlearn"?
Phew! The list just goes on and on. What an incredible challenge. Plus, still meeting assessment and data requirements that fulfill National Standards requirements.
Really, the 21st century teacher needs to prepared to "let go" of lots of established practice that has been embedded/ingrained in us for many many decades. In letting go some prior practices, they will be able to venture into new practice. It's a shift from "transmitting" knowledge and assessing student performance in set ways to working with students' strengths to see what they are capable of.
What needs to happen to allow these conditions to occur? I think the way we plan would need to change. Students would need to have a lot more input into the structure of what they were learning and how they might show their learning to others. Certainly assessment practices would need to be changed in many cases. Teachers would need to be able to focus on what the student has got better at, rather than deficit thinking practices.
So if we could "redesign" schooling, what would we change? If we could start from scratch (we still have the same buildings) and ask, how would our school run and what would students do if we knew nothing of requirements, policy and forgot all our current practices - what would our school look like?
How do we shift our culture based on what we really truly believe and what we want to achieve for our learners?