English Government Report into Early Language Learning   - hgunn.uk

This Report that has been written by the Education Endowment Foundation and Public Health England. They claim that low vocabulary at school entry correlates with adult literacy at 34 years of age and mental health and employability. It argues there is some evidence this problem runs in families and twin studies illustrates high levels of hereditability.

 They suggest that the quality of input may be more important the quantity of it. It reports that 70% of preschool children with low language skills resolve them and 30% do not. 

Garthcole and Alloway (Click)

Classroom Guide - Detailed Report

 This is a publication on working memory for schools. It explains that working memory varies amongst people and is relatively fixed.  It explains the spread and growth of working memory as children grow older. It explains that some children have difficulty in retaining a simple instruction in their working memories

This Sweller Cognitive Overload (Click)

 Classroom Guide

Cognitive overall is the study of how working memory can be overloaded.  It is not an exact science, but the more than the extraneous load, the load upon working memory that is not necessary for learning, the more working memory space will be available for learning.

H.G. Sadly, expecting children to learn and to be educated through the medium of Welsh is an extraneous load. It is not necessary for learning.