This old study aid for math turns out to have a scientific basis

Since the early 20th century, teachers at Montessori schools have taught reading and math by having kids trace letters and numbers with their fingers. This trace-to-learn idea, which has become semi-legendary among students, now appears to have some scientific basis. A group of Australian researchers found that kids who learn mathematical formulas while tracing the outlines of shapes are able to understand and recall their lessons more easily.

University of Sydney educational psychologist Paul Ginns worked with 279 students between the ages of nine and 13, teaching them algebra and geometry by asking them to trace over practice examples with their fingers while reading about the underlying math. Students might trace a triangle while learning the Pythagorean Theorem, for example. After tracing, students recalled the math more easily and gave correct answers about it more often than students who did not trace.

Ginns, who studies memory in learning, believes that the physical act of tracing may give the task "processing priority" in the brain.