Graphomotor and handwriting disabilities (GD and HD, respectively) could significantly reduce children's quality of life. Effective remediation depends on proper diagnosis; however, current approaches to diagnosis and assessment of GD and HD have several limitations and knowledge gaps, e.g. they are subjective, they do not facilitate identification of specific manifestations, etc. The aim of this work is to introduce a new scale (GHDRS--Graphomotor and Handwriting Disabilities Rating Scale) that will enable experts to perform objective and complex computer-aided diagnosis and assessment of GD and HD. The scale supports quantification of 17 manifestations associated with the process/product of drawing/handwriting. The whole methodology of GHDRS design is made maximally transparent so that it could be adapted for other languages.