@polotek When I worked at Fitbit, the company had Ken Rubin teach a 2-day agile training once a quarter to new hires. This gave everyone a shared, foundational understanding of how to break problems down into known knowns and unknowns, how to estimate effort or timebox until able to estimate effort.
Many of us were skeptical at first, but we did actually get much better at estimating at the team level. Success was how accurate the team was in delivering the work committed to in a 2 week sprint.