Prewriting shape (left diagonal line)

Why is it important to master the prewriting shapes before beginning formal handwriting instruction?
There are many reasons! These shapes are the components that make up every letter in the alphabet, and they serve to provide an opportunity for parents and/or teachers to establish a way to describe direction to a child so that when you start describing the more complex combinations of prewriting shapes that make letters, our students will already know what “a long line down” looks like and feels like, and how it is different from a slanted or an intersecting line. It also helps us to start pointing out the comparison of size and space taken up by a shape on and how it is positioned and oriented on a background: This spatial awareness is fundamental to developing the more advanced skill of placing letters on a line as well as comparing the “tall letters” to the “hanging letters” and “short letters” once we start combining letters to make words.
Practicing these shapes separately before tracing, copying, or writing letters also gives us a way to make sure we have reinforced a functional grasp on a variety of writing tools—students write with many sizes and diameters of markers, crayons, and pencils in a classroom on a daily basis and we help ensure their hand strength and visual motor skills are well enough developed that we can introduce letter writing without having too many new concepts to focus on all at one time. Too many students become frustrated by the difficulty of writing without the aforementioned pre-requisite skills and become reluctant to practice writing.
If you are interested in more information about pre-writing skills and the pre-writing shapes, here are some links that you might find helpful:

The companion path of motion visual as well as the corresponding verbal cues are available here: