Hypothesis
Accumulated deliberate practice would differ by skill level among student violinists, as in Ericsson et al.'s (1993) seminal study.
What failed
With a double-blind procedure and analyses suited to the design, the core finding that accumulated deliberate practice corresponded to each skill level did not replicate; the effect was substantial but considerably smaller than the original. Teacher-designed practice did not explain more variance in performance than practice alone.
Broken assumption
Differences in accumulated deliberate practice largely account for differences in expert performance.
Why
The paper reports a smaller effect than the original under tighter methods; it does not attribute the difference to a single cause and discusses the implications for deliberate-practice theory.
From the published paper: Macnamara et al. Royal Society Open Science, 2019. ↗CC BY