An experiment is designed to compare the differences in learning outcomes between learning math from s video game and learning it from traditional classroom activities. the experiment finds no difference between the two. what was the dependent variable

A dependent variable is the what is measured in the experiment. It is affected by changes in independent variables. 
In this experiment, independent variables are environments in which students learn. 
A dependent variable would be something that indicates how much math they learned in those two environments. 
This could be a number of questions answered on a test.