Two families are keeping their nine children home from an island school amid concerns about a 5G mast on the building.
It was put up at Stronsay Junior High in Orkney as part of a BBC trial testing live radio broadcasts over 5G mobile networks.
The trial was initially due to run for six weeks but was later extended until the end of September.
Some parents are concerned about potential health risks.
One family withdrew their three children last term while another family did not send their children to school yesterday.
Their father, Duncan Bliss-Davis, whose six children are aged five -11, said they were concerned about potential risks.
He said: “The NHS are saying children should only use mobile phones for essential purposes and keep calls short and Public Health England says excessive use of mobile phones by children should be discouraged, yet there is a mast on the school. One of the reasons we moved here was to get away from the explosion of mobile phone masts and mobile phones.
“People keep talking about how we’ve been using phones for years with no ill effects but my point is that is not for a person’s lifetime.”
The children are being home schooled but Mr Bliss-Davis said they will probably go back if the trial ends in September.
In a letter to parents, the BBC said: “The equipment we’re using is based around 4G technology, which is widely used across the UK, and the radio frequencies used are the same that are used to broadcast TV.
“The trial is fully compliant with advice from Public Health England”
Orkney Islands Council said it worked with the BBC to identify Stronsay, which has poor connectivity, as a suitable location.
A council spokesman said: “The council obtained guidance on 5G safety from (PHE) before agreeing for the 5G equipment to be installed.
“PHE is the national body that takes the lead on public health matters involving radio frequency electromagnetic fields, or radio waves, used in telecommunications. “PHE’s advice is that there should be no consequences for public health.”