This photo from Asahi Shinbun (2/28/2012) shows a giant radiation monitoring and display device on the school yard which looks like it has been "decontaminated". 0.227 microsievert/hour (most likely measuring only gamma rays), children, feel free to run around and kick up dust in the new and improved school yard...
(To recap, this is how they "decontaminate" in Minami Soma.)
This monitoring and display device was made by Fuji Electric. Alpha Tsushin (telecom), the company who was initially contracted by the government to build and install radiation monitoring and display devices throughout Fukushima Prefecture, was suddenly dropped from the contract in November last year because the reading of their device was "inaccurate" - meaning it was "too high" for the government.
The schools that re-opened in Minami Soma City are located in Haramachi District of Minami Soma City where the "black dust" on the road surfaces was found with 1 million becquerels/kg of radioactive cesium.
There are some very strange things going on over the "black dust" in Minami Soma, and I can't really quite get the whole picture yet. I'll report when I have a better understanding.