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.

Source: http://arstechnica.com/science/2016/01/this-old-study-aid-for-math-turns-out-to-have-a-scientific-basis/