This pamphlet outlines an attempt to provide an instrument by which the linguistic background of Welsh children can be measured. In a group of Welsh-speaking children there are different degrees of Welshness, and it is essential, for educational purposes, that the degrees of Welsh linguistic background be estimated. The two versions of the Welsh Linguistic Background Scale, one in English and one in Welsh, are included, and instructions for their administration are given both in English and Welsh. Instructions for scoring follow. The validity and reliability of the scale have been tested and confirmed. The results from such tests would aid in student placement, later in job placement, and in the standardization of intelligence and attainment tests. Apart from its use as a necessary tool for research, the scale is recommended as a practical guide for teachers and others who are concerned with school organization. (Author/TL)