A system includes a brain activity sensor sensing electrical activity of a students' brain and a device that receives messages from the brain activity sensor while the student is receiving instructions with a first value for an attribute of instruction and that determines a first attention level from the received messages. The device receives additional messages from the brain activity sensor while the student is receiving instructions with a second value for the attribute of instruction and determines a second attention level from the additional received messages. The device then determines an attention variability for the attribute of instruction based on a change in attention level from the first attention level to the second attention level.