Find examples that use only straight lines to display an idea and show them to the class. With the class, discuss why the piece is done with lines, and what effect it would create if done differently. Challenge the class members to do their own art pieces using nothing but straight lines. Cut paper is a good medium to start with because you can arrange it before permanently attaching it to a surface.
Discuss the basic vocabulary of lines. An edge, for example, is formed when two different value areas or surfaces meet or intersect, according to Design Principles and Problems. Although an edge is a type of line, it can only be created when two different values are placed close together, and not by drawing a line on paper.
Find examples of artistic pieces that use curves. Because they are still manipulating lines, they are an effective way to illustrate the vast difference between what a line can do and what a curve can do. Discuss with the class what the effect of the curves is. Have them create something using the same techniques and then, as a class, critique everyone's individual pieces.
Give the class more vocabulary to help them distinguish between the types of lines. A tightly controlled line has sharp edges and contours, while a freely gestured line moves with grace and has many more curves. Talk about lines that display emotions: a squiggly line may be curious or angry depending upon how sharp the edges are. A line that is scribbled uncontrollably may express chaos. Because art is very subjective, tell your students that it is okay for them to see different emotions in the same line.
Give the class a major assignment or project with the criteria that it must illustrate an idea using only black lines on a white surface. It is important that the lines are not colored so the students won't be more concerned about the colors than the lines.
Critique these projects one at a time in front of the class by placing them on the board or pinning them to a wall. Talk about how the pieces could have been different, and why the lines are positioned the way they are. Talk about the line size, length, width and position (horizontal, vertical or diagonal) and how they work together.