The quality or state of being formative; the degree to which something shapes or influences development.
From 'formative' plus the suffix '-ness' (creating an abstract noun). This is a relatively rare word, but follows standard English word-formation patterns.
The 'formativeness' of early education—how much it actually shapes children's development—is a major focus for educators and psychologists worldwide!
Complete word intelligence in one call. Free tier — 50 lookups/day.