The authors note that purposeful practice can result in getting stuck if you learn bad form (they don't use that term, but what they describe is very close to the concept of "good form" from the CFAR handbook (page 19)). Bad form means that practice is ultimately instilling bad habits, even if it creates local improvement. Good form means that practice is taking you down the path to mastery in an efficient manner.
Due to the necessity of having an experienced teacher, deliberate practice requires a highly developed field. However, it is also common to use the term "deliberate practice" for anything which is distinguished from purposeful practice by the presence of a theory of skill and practice guided by that theory, whether or not that theory is tried-and-true, and whether or not an experienced teacher is involved.
Deliberate practice is the highest form of practice according to Anders Ericsson and Robert Pool (the authors of the book Peak). Based on the scientific study of expertise, they classify several forms of practice. From less to more effective:
Should this tag only posts specifically tackling deliberate practice as a topic in itself, or also posts discussing the application of deliberate practice to X skill?