Teachers have been "guaranteed" improvements to Covid-19 policy in schools, according to the TUI.
Last week's peak saw up to 16,000 children self isolating after being deemed a close contact of a positive case.
Michael Gillespie, general secretary of the TUI, has labelled last weeks events as "unacceptable".
Speaking on Newstalk on Monday, he said: "Last week what we saw was unacceptable and hugely stressful delays for principals seeking information, especially early in the week.
"We made strong representations that this should cease and we have been guaranteed that improvements will be made.
"Now, anybody could have saw that surge coming. Demand for testing during the first two weeks back with students returning to school.
"What we're waiting for now over the next two weeks is the results of those tests, they're going to come after five and ten days. And we'll see how the Delta variant is spreading.
"We're waiting to see how that testing turns into numbers."
Mr Gillespie said that any changes made to close contact testing must be based on public health advice.
"If there's going to be any change in close contact testing it must be based on sound public health advice and because there are any deficits in contact tracing.
"We hope that it will be low numbers that turn into positive cases, but we need the figures to support that."
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