its not slave labor if the laborers get something in return

sure the students don't get paid money but they learn important skills that are much more difficult to teach in a classroom. These students are learning to be scientists, scientists do experiments, therefore the students need to learn how to preform experiments either by A) doing experiments or B) sit in a classroom as some guy explains how to do an experiment.

Also, to be employed as anything other than a high school science teacher, it is important for any scientist to publish. Doing experiments like these allow students to get their names out in the field and hopefully land a decent job.

So if you have a better means to educate scientists id love to hear it, but frankly this method is the most effective one i've seen