Strike affects over 200 schools across Kent and Medway
Rallies have been held across Kent as thousands of public sector workers protest over future pension plans.
More than 200 schools across Kent and Medway were closed or partially closed by strike action involving two teaching unions.
Port of Dover authorities said it was "business as usual" with no delays. Traffic was also "flowing freely" though Calais, a spokesman said.
Protests were held in Chatham, Dover, Maidstone and Sittingbourne.
Across the UK, up to 750,000 teachers and civil servants are on strike over planned changes to public sector pensions.
Unions said the changes meant teachers paying more, working longer and getting less.
Sarah Hohler, of Kent County Council, said about two thirds of the county's 592 schools had opened.
She said: "I think that's really good news and a credit to our teachers.
"It shows their commitment and respect to our pupils and their parents to have kept so many schools open."
A Conservative MP who said she would be taking the day off from Parliament to help keep children in classes said her services had not been required.
Tracey Crouch, who represents Chatham and Aylesford, worked as normal at Westminster.
She had offered to help a school in her constituency so that classes were not disrupted.
But Ms Crouch said local head teachers had told her that either their schools were closing or they had already found alternatives to keep them open.
She said: "I think it's rather disgraceful and distasteful for unions to claim success for disrupting a child's learning when actually we should be paying tribute to the teachers who continue to keep their schools open."
The impact of the co-ordinated industrial action began to be felt at ports and airports on Wednesday evening, when some UK Border Agency staff walked out from 1800 BST.
The Public and Commercial Services Union (PCS) said Dover was going to be one of the worst affected ports in the country, but the Port of Dover authorities said operations were running as normal.
The high-speed Channel Tunnel train company Eurostar said it was not affected by industrial action and planned to run two extra trains - one from London to Paris, the other from Paris to London, to cope with expected extra demand.
Simon Marchant, who works at Canterbury College, was taking part in a rally in the city.
He said: "Whatever way you look at it, we are being asked to pay more now to receive less later."
The Conservative MP for Canterbury Julian Brazier said the current system was not fair to "all those struggling people in the private sector".
He said private sector workers did not have the same job security and were on lower incomes.