The phrase "full mastery" means having full control, knowledge, or expertise over something. It means being able to do or understand something very well and being in complete command of it. Full definition
This is the poet as conceptual artist, in full mastery of her craft. (nytimes.com)
Full mastery data is available on the online parent portal. (teacherease.com)
Additionally, it will guide students in understanding what full mastery of a standard is, and it will keep parents informed about student progress. (imagineandrews.org)