Andy Henion:

Students perform better in math when their instructors use hand gestures–a simple teaching tool that could pay off in higher-level classes like algebra.
The study published in Child Development [1] provides some of the strongest evidence yet that gesturing may have a unique effect on learning. Teachers in the United States tend to use gestures less than teachers in other countries.
Straight from the Source
Read the original study [1]
“Gesturing can be a very beneficial tool that is completely free and easily employed in classrooms,” says Kimberly Fenn, study co-author and assistant professor of psychology at Michigan State University. “And I think it can have long-lasting effects.”
Fenn and her colleagues conducted an experiment with 184 second, third, and fourth-graders in Michigan elementary classrooms.
Half of the students were shown videos of an instructor teaching math problems using only speech. The others were shown videos of the instructor teaching the same problems using both speech and gestures.
The problem involved mathematical equivalence (i.e., 4+5+7=__+7), which is known to be critical to later algebraic learning. In the speech-only videos, the instructor simply explains the problem. In the other videos, the instructor uses two hand gestures while speaking, using different hands to refer to the two sides of the equation.