The Department of Health and Social Care in England has apologised "unreservedly" for emails sent in error to schools in Northern Ireland.
Schools received an email from the department on 5 September about supplies of Covid-19 home testing kits.
They referred to schools as "care homes" and said kits would be delivered on Monday 7 September.
The Department of Education (DE) subsequently called the email "regrettable".
It said it had been sent by the Department of Health and Social Care (DHSC) in error.
On Wednesday evening, DHSC contacted school principals in Northern Ireland to apologise.
They said the earlier emails had been triggered automatically and sent in error.
"They do not reflect the guidance that schools participating in the initiative are required to consider and follow," DHSC said.
"It is also our understanding that a number of you have already received kits, contrary to the Department of Education's request that this should not happen at this point.
"Officials from the Departments of Education and Health have been in contact with us and have expressed the levels of frustration felt by education settings and the trades unions about these issues.
"We want to take this opportunity to apologise unreservedly for the confusion caused by both the emails and the deliveries, and for the unnecessary contact at a time when your focus is rightly on the wellbeing of children and staff and the safe restart of schools".
DHSC also said they had taken action to ensure no further emails would be sent, and that guidance would be sent from the Department of Education in Northern Ireland to schools about the home testing kits.
Schools in Northern Ireland are to get 10 home testing kits for parents of pupils with symptoms of Covid-19.
The kits are intended to allow families who cannot travel to a testing centre to carry out a test for coronavirus.
On Wednesday, it was revealed positive Covid-19 cases had been reported in 64 separate schools in NI among staff or pupils in the first two weeks of the school term.