Because wireless routers (there is one about 2m away from me right now) emit microwave (radio) radiation, this is very likely the case that there is a biological effect. The study you cited was done by 9th graders. That does not mean the study should be dismissed
Here is the result of another informal study (a school science project it would look like) reported on a Canadian website (with pictures) showing the effect of seed growth near a cell phone and near a router, and with a control: www.odec.ca/projects/2009/bail9m2/index.htm Note that the student had some caveats about the quality of the control as the experiment did not completely confirm his hypothesis.
