The result of over twenty years of research, the Common European Framework of Reference for Languages: Learning, teaching, assessment (CEFR) is exactly what its title says it is: a framework of reference. It was designed to provide a transparent, coherent and comprehensive basis for the elaboration of language syllabuses and curriculum guidelines, the design of teaching and learning materials, and the assessment of foreign language proficiency.
From the page: "Children whose father's vocabulary was more varied when they were 2 years old had more advanced language skills at age 3. Surprisingly, the dads spoke less and asked fewer questions than the mothers, suggesting it was not how much they spo