Parents and pupils queued outside the gates as schools started to reopen in England and Wales.
Meanwhile, students in some parts of the UK have returned to school for the first time since face masks were made compulsory in communal areas to combat the spread of coronavirus.
There was a long line of pupils and parents at Bishop Road Primary School in Bristol as it welcomed back more than 800 children.
Arrivals were split into two groups – before and after 9am – to allow staff to direct pupils to the correct classroom.
Only a few parents chose to wear masks while entering and exiting via a one-way system.
Parent Amanda Lewis, 44, who runs a martial arts school, said: "I think most parents are relieved – we've had a very long time with them.
"My son has really, really missed it – that environment. Their home is supposed to be a safe place, not somewhere where they are told to have stringent routines.
"I had started to worry about his emotional health, being at home. I'm relieved they've gone back in.”
Secondary school students over the age of 12 in Scotland and Northern Ireland must wear face coverings in corridors and other areas outside classrooms.
The new rule came into force on Monday and thousands of pupils in Scottish schools moved between classes while wearing masks.
About 300,000 pupils in Northern Ireland also returned to school on Tuesday, many for the first time since the coronavirus lockdown was introduced in March.
In Scotland, masks are also mandatory on school buses.
Pupils do not have to wear masks in the classroom, where social distancing is in force.
In England, following a U-turn by the government, face masks are only mandatory in schools in an area under local lockdown restrictions.
For other schools, headteachers can decide on what mask rules to introduce for pupils and teachers.
In Wales, the decision on wearing face masks has been left to individual councils and schools.
Students in Scotland have been back at school since 11 August.
On Tuesday, the Scottish government revealed that more than one in 10 pupils had been absent from school at the end of last week.
However, of the 73,000 absences, it said only 21,800 were related to COVID-19.
The World Health Organization has recommended that children aged 12 and over should wear face masks.
Coronavirus: what happened today
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