That's not the best approach to teaching art, imo. By "correcting the form of their drawings" you're stating there's something incorrect.
My goal has always been to encourage students to love art. It's something you can do for a lifetime unlike so many other activities. Plus unlike math where 2 + 2 will always = 4, there is no wrong answer in art.
Sure, I could create a rubric so onerus that a child could never achieve success, but that's not what art class should be about. Again, imo. So, no, "correcting the form of their drawings" is not on my agenda or a part of my curriculum. Encouraging them to develop their own style? Yes. Assisting them if they ask for that assistance? Certainly.