Sarah, we have faced the same problems. Estimation is a skill that people have to work to improve, regardless of the units they use to express the estimate. We standardized on Fixed Work, Effort Driven because it allowed us to all speak in the same terms, but there’s nothing magically better about this method. I do like it because there is a nice correspondence between the estimated and the actual work. It seems to convey more task ownership when I can see my original estimate and the actual time it took me, right there. If I say “give me a week”, I’ll know if I miss the end date, but I’ll learn nothing about why.