A new £28m school campus in Dumfries has been closed on safety grounds after a second incident within two weeks.
The EIS teaching union said an interactive whiteboard had fallen on a pupil in a class.
Contractors Graham said it had immediately investigated and concluded "excessive force" had been used on the sliding smart screen.
The same campus was closed last month after a pupil was struck by a sliding door which came off its rails.
Dumfries and Galloway Council said it had "lost confidence" in assurances it had been given over the North West Community Campus in Dumfries.
The facility opened to pupils in August despite concerns a few weeks earlier, when it was claimed a ceiling had collapsed.
A subsequent investigation blamed the issue on an error fitting a sprinkler system which had caused "sagging and superficial damage".
The school opened in time for the start of the new term, but was then closed for two days after the incident involving the sliding door.
The council said it was "appalled" by the latest incident, but declined to comment on reports that another child had been hurt.
It is understood the boy was not seriously injured.
The council said it would not reopen the school until it was "absolutely confident" and had independent assurances that "every bolt, screw and fitting" had been certified safe.
"An incident response team has been set up to assure the continuity of pupil education," it added.
"The young people of north west Dumfries deserve much more and we are angry and disappointed at the disruption to their education."
The EIS and Unison unions both welcomed the decision to shut the site.
"There have been a series of incidents at the NWCC, which have left staff deeply concerned about safety," they said in a statement.
"We understand that Health and Safety Executive officials will visit the NWCC next week and our health and safety representatives look forward to engaging with them."
The contract company Graham said it had investigated the "unfortunate incident" and had examined the screen and its mounting brackets along with experts from the installation company.
"It's clear from this examination that the screen was subject to a very high level of excessive force, which caused it to separate from the bracket," a spokesman said.
"We have also examined the remaining 20 screens in the school and all are functioning normally, and in line with the strict tolerances and operational guidelines."
He said it awaited the outcome of the council's investigation into the circumstances.