How to compare four sets of experimental data and decide if the differences are significant?

For a school science fair project, my daughter randomly divided a population of subjects into a control group and three experimental groups. We recorded the time each subject took to perform a certain task. Now we want to analyze the four sets of time data to decide, for each of the three experimental groups, if subjects in that group took more or less time overall to perform the task than subjects in the control group.

What is an appropriate procedure for comparing the times between two groups, and how do we decide if the difference is significant?

Perhaps there is some method that takes into account the difference in two groups' mean times, and compares the difference with the overall dispersion of the times? But if so, I don't know what it is or what it is called. A pointer to the literature (or to Wikipedia) would be helpful.

I have a strong mathematics background, but I don't have any specific expertise in statistics.