Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said secondary schools would inevitably lag behind primary schools.
He told BBC Breakfast on Saturday: “It’s not going to be life as normal.
“I think for primary children they will largely be able to go back into their primary schools and although it’s not going to feel absolutely normal, teachers will start to get them back into the rhythms and routines that will be, for the majority, exactly what they need.
“Secondaries are a different issue. MASH-style field hospitals essentially are having to be set up in order to do these lateral flow tests.
“We shouldn’t expect that on the 8th all pupils will be back in, it will be from the 8th because we have to get those tests under those young people’s belts first.”
Mr Barton warned that further loosening of lockdown measures would not go ahead unless the first phase of reopening of schools was successful.
He said it was “a national moment on which much depends”, adding: “You were talking earlier on about festivals, etc, happening in the summer, nothing is going to happen, including retail, unless we get this first phase correct.”