Scratchy chalk is low-quality chalk or poor technique. Every writing instrument has its own techniques. Like how fountain pens work better at a lower angle and lower pressure, and ball-point pens work better at a higher pressure and the angle doesn’t matter so much.
Or poor quality boards. I know I didn’t use a real slate board until later in university and it makes a world of difference. Really you need both, great chalk and a great board. But when you have both the feel is superb :)
