It has been a few years, and this study was recently brought to my attention. I found the same information mentioned by @MrOoijer, but there has now been time for attempted replication studies to be performed. The first I found was:
Effects of Wi-Fi Radiation on Germination and Growth of Broccoli, Pea, Red Clover and Garden Cress Seedlings: A Partial Replication Study
--Magda Havas and M. Sheena Symington
Current Chemical Biology, 2016, 10, 65-73
This paper appears to confirm the general results. I have yet to see a good analysis of this paper's methodology. It's an open access article, and it seems the publisher has been accused of skipping or rubber stamping peer review before on an open access journal  but obviously it's difficult to tell what level of scrutiny this paper received. They do attempt to track the parameters that were criticized in the high school study. The 1st author, Magda Havas, has been publishing for some time on this topic, specifically on 'dirty electricity' in addition to other toxicology studies.