She packed in her job at Latchmere Infants School in Kingston, Surrey, but had no intention of retiring. Instead Mrs Steinthal, 52, set about realising a lifelong dream of starting her own alternative school.
She and husband Peter, an accountant, ploughed their life savings into buying and converting an old Baptist church in Cowleaze Road, Kingston, and in March this year Educare Small School opened its doors for the first time. It started with just two pupils; now there are 20. Mrs Steinthal, currently working without salary, is optimistic that before long she will reach her target of 50 pupils between the ages of three and 11.
"We knew there was a need for a new school and parents were crying out for an alternative, but we didn't know how successful we'd be," she says. "Now it's really beginning to happen."
The idea grew from Mrs Steinthal's concern that large numbers of children are being failed by the state system. Many children, she says, find it difficult to keep up because classes are so big. They start to fail and feel they are failing, and this has a knock-on effect on how they approach secondary school and then enter society.
She feels this is particularly true of middle-class north Kingston, despite the borough's impressive national test results. Schools perform well because of the level of parental support, she says, but national figures fail to reveal the significant minority of children who fall by the wayside because of the area's high pupilteacher ratios.
"I taught mainly six and seven-year-olds, and there was always a level of children who were not managing to keep up and whose self-esteem was totally gone. I spent nearly the whole year restoring it before I could attack what were basic literacy problems. There were too many children at the beginning to be able to focus on individual needs."
She does not believe the Government's pledge to reduce classes to no more than 30 for five, six and seven-year-olds will make much difference. "Classes of 35 are ridiculous, particularly for very young children, but it's still difficult to teach 30 children at different levels," she says.
At Educare Small School, pupils are taught in groups of no more than five or six. They follow the national curriculum and, says Mrs Steinthal, do all the things parents expect - but they do not sit national tests.
"The tests are no use, and league tables are an abomination because they make schools focus away from what's correct for the individual child," she says. Her school is unashamedly non-competitive. "We're not academically driven. There's more to life than qualifications and exam results.
"If a child takes until he or she is seven or eight to get basic literacy skills, then that's what they need to be doing. We're about developing the whole child and moving at a pace that's comfortable."
Another unusual feature is the school's emphasis on meditation. There is a "quiet time" in the middle of each day when pupils lie on their backs for 10 to 15 minutes with their knees up, listening to music and reflecting.
It wouldn't be to every parent's taste, but Mrs Steinthal insists there are benefits. "It's one of the most enjoyable parts of the day. At the end,we have a quiet, focused group ready to concentrat e on the next activity."
An Alexander technique teacher has also been taken on once a week to help children with posture, breathing, poise and balance, the idea being that if a child is physically relaxed he or she will learn better.
The fees - #163;850 a term - are kept to a minimum to make the school as accessible as possible. So far, this seems to be working: parents range from bikers to architects.
Mrs Steinthal, whose three grown-up children went through the state system, admits she has never been a fan of independent schools, and if money were no object the school would be free.
"What we really need is central government funding, which you get in countries like Denmark where parents can set up their own schools and run them as a small community," she says.
Days for the school's three staff, including Mrs Steinthal, are long. Teaching is from 9.15am to 3. 30pm, but the school is open from 8am to 6pm to cater for working parents. Despite the workload, Mrs Steinthal, a member of the Human Scale Resources organisation, which promotes small schools, would not go back to the state system.
"What I do now isn't stressful, because there's not the endless pressure of trying to deal with a problem that's almost impossible to solve due to lack of funding."
Mother-of-three Giselle Luxford, 40, from Kingston, recently removed her five-year-old, Georgina, from the local primary and sent her to Educare. "Georgina hated the large assemblies with hundreds of children and found her class of about 35 daunting," she says. Ms Luxford has nothing but praise for Educare's methods and philosophy. "Georgina settled in immediately. The school's home from home, like going from one mum to another."