If Debbie Morris thought she’d got out of PE with Year 10 when she “forgot” to bring her sports kit to school, she was sadly mistaken. “I looked outside this morning and the weather looked really miserable so I didn’t bother to bring it,” she said.

If she thought the oldest excuse in the book was going to wash with the sports staff at Farlingaye high school, it showed how long it was since 31-year-old Debbie left school. A quick rummage round the locker room and they soon came up with a pair of trainers and a sweatshirt and leggings.

Debbie was discovering the hard way what school life is like in 1997 for her step-daughter Emma and the other 1,244 pupils at the school in Woodbridge, Suffolk.

After the success of Take Your Daughters to Work day, the comprehensive has started holding Take Your Parents to School days. No open days these, with teachers and pupils on best behaviour, timetable suspended. This is the real thing, Farlingaye warts and all - and parents are expected to muck in with whatever their children do.

Gordon Walker felt a bit sheepish. He had just been beaten by his son Alaister in a Year 8 English test on word definitions.

“I was extremely lazy,” he admitted. “I should have looked the words up. It was a test to encourage them to use a dictionary. Everybody did except me. Alaister got nine out of 10; I got seven.”

A leading parent-teacher association member and the school’s industrial link through his Ipswich business, Gordon had never sat in on lessons before.

Like most of the 40-plus parents accompanying their children, he was amazed at how things have changed. The children are more confident, happier to speak up in lessons (despite claiming to be “embarrassed” that Mum or Dad is there) and the teachers are friendlier. The whole atmosphere at school is more relaxed than anyone remembers.

Deborah Villiers, following her son Nicholas through the surging tide of children between lessons, remembered her old school in Wales. “We had one staircase for boys and one for girls. You had to walk on the left and put your bag over your right shoulder so as not to scratch the walls. All those little rules I” Nowadays, children come first, the buildings second.

The day - likely to become an annual event - is a sign of the self-confidence of the Woodbridge school, which parents say is blooming under the headship of Sue Hargadon. The Office for Standards in Education delivered fulsome praise after an inspection last month, saying teaching in two-thirds of lessons was good or very good.

“What’s interesting is the number of parents who say they feel tired at the end of the day,” Ms Hargadon said. “I think the day strengthens the home-school partnership. It gives parents a real insight into what a day in the life of the school is like and a chance to see the very positive atmosphere.”

Science lessons - one area where you might expect things to be radically different - were reassuringly familiar, as pupils dissolved rock salt and distilled pure water.

But, elsewhere, parents were surprised at how different the curriculum is these days. Old girl Susan Potter still remembers baking cakes in domestic science lessons 25 years ago. Now, with son Gavin, she was exploring the world of food technology. That meant taste-testing mini Mars bars, along with discussions of product packaging and the addictive properties of chocolate. When Susan Potter finished her work, teacher Katie Boswell stamped “Wicked” in her exercise book.

Deborah Villiers was delighted to find Nicholas studying the Spanish architect Gaudi in art. With relish, she spent the double lesson making a Gaudi-esque clay tile from her son’s designs. “Gaudi was a very exciting architect. Maybe we’ll have some decent buildings when they leave instead of the same square boxes.”

English proved just as challenging for two dads, Alan Burchell and John McCarthy. They spent a lesson with Year 7 imagining what it would be like to be a tennis racket and a musical instrument locked in a cupboard. Having just 12 minutes to write an essay and then read it out gave them pause for thought.

“I was trying to think whether at that age I was writing that sort of thing, ” said John. “Probably not. There was a lot of imagination in the pupils and they’re being encouraged to use it.”

Charles Fear, the energetic head of English, has written a dissertation on the relationship between parents and secondary schools. He argued there has been a three-way conspiracy of misunderstanding: pupils don’t want their parents to know what they are doing at school; teachers don’t want parents to interfere, and many parents are happy to let schools get on with it. “Parents have been excluded for the past 40 years and they have connived in it,” he said.

Ms Hargadon believes this is no longer the case. In recent years, schools have tried to involve parents more. “Being a parent myself, I know you often wonder what your children are like at school. I thought it would be lovely to let mums and dads sit and watch.”