While one headteacher in the area says his school has benefited from the LTN, most say they've seen "huge increases" in lateness, bringing operational problems, stress and anxiety into their schools. Journey times have eased this week, following the removal of roadworks and in the approach to Christmas, but schools are still encouraging parents to put pressure on Lambeth Council to avoid more gridlock in January.

Some parents living outside Streatham have already made the decision to move their children - and the several thousand pounds of government funding that goes with each one - since the start of the LTN scheme in October, which seems to have been the catalyst for exponentially higher journey times for those trying to navigate Streatham in rush hour.

It's a worry for heads, especially with pupil numbers already under pressure. Fewer pupils means offering less to those who remain. "If you don't have a full roll, you can't sustain your provision," says one.

And they're concerned that staff will start moving away from Streatham's schools, because they can't reliably get in on time, especially when they have to get their own children to schools and childcare first. "Recently retention has been very good," says a headteacher, "but staff are now looking elsewhere."

Many public-sector workers live south of Streatham - "They can't afford to live in Streatham, I can't afford to live in Streatham," says one head - and it has been "almost impossible to get a bus from Croydon".

At one school, a local member of staff last week took nearly two hours to get into work, arriving after the start of school and more than an hour late for the typical start of a teacher's working day at 8am. "She had to drop a child at school, one at nursery, and then couldn't park because of the school street," the head says. "She was so stressed when she arrived."

Lateness of both adults and children is "the biggest trigger" for stress that is then brought into classrooms, the head says. "As soon as a parent realises they're going to be late, stress levels rise, children pick up on the stress, it causes arguments. It's causing a lot of anxiety for children and parents."

Other headteachers also report staff being late for the school day, and say they've seen substantial increases in pupil lateness figures. "There's been a huge increase in the number of children who are late, and also the collection times have risen ridiculously."

Schools are in "full support" of their school street schemes, which see some roads next to schools closed to through traffic at the start and end of the school day, and support environmentally-focused goals of sustainability and "active travel" as part of their curriculums.

But they worry about the impact of this latest LTN, and that many in the community just won't be able to find workable alternatives to driving. They point to Streatham's access to public transport being worse than in many parts of London, with no tube or trams, and train services that have often proved themselves unreliable.

"We are very committed to the sustainability agenda of our local area," one school has written in a letter to parents, "but it is clear that this needs a carefully planned, holistic approach."

They're not yet seeing any "active-travel" advantages. "We do have some kids cycling into school but we haven't seen an increase in that." Congested traffic on and beyond the LTN's boundary roads and an assumption of higher pollution levels are likely to put parents and children off from cycling, they suggested. "The roads are really dangerous now, people are taking more risks," says one. "They'd just be cycling through fumes," says another.

On top of the traffic problems, some headteachers are also worried that Lambeth is cutting back on parking permits for staff, where it is rolling out controlled parking zones (CPZs). The permits are now only sold to fully-qualified teachers, with support staff finding themselves unable to renew theirs.

And they're concerned that the quietness of the LTN's streets could enourage an increase in crime against their communities. Some staff are being advised to leave their schools in pairs to walk through the LTN - "there's no passing traffic and people feel vulnerable" - while one headteacher has said in a letter that they have "written to our local MP and Police Sergeant about the issues of crime on the High Road, and the potential for more muggings now that there are no cars on the roads of the LTN".

"I understand the need for sustainable transport," says one head in conclusion, "but this feels like a punishment."

Traffic outside the school has fallen "significantly", executive headteacher Chris Ashley-Jones said in an interview with Lambeth Council deputy leader Cllr Rezina Chowdhury, which the council posted to its YouTube channel.

"That 20 minutes or half an hour of extremely busy and dangerous traffic has gone down to about one minute, if that, and some days we don't get it at all. So it's been a massive improvement," he said.

The school sits back from Leigham Vale. The road wasn't itself blocked off by the introduction of the LTN, but the closure of Valley Road to through traffic means that there is now no sensible though-route past the school for vehicles travelling south to north.

On the day that Cllr Chowdhury visited Hitherfield and its Christmas fair, she was also expected at a similar event at Julian's Primary School on Leigham Court Road to get "feedback" on the LTN scheme, but didn't arrive. A council spokesperson said they would check why Cllr Chowdhury's plans changed, but has given no further response.

The council is scheduling a first formal "engagement" process with "key stakeholders", including schools, for the end of January and early February, when the LTN will have in place for three months.

She recently moved out of Lambeth to just inside the Borough of Merton, and needs to get north and east across Streatham every morning to drop two children at two different schools, before getting back west again to catch a bus to St George's, where she works for Macmillan in the oncology department.

Her family in Lambeth can look after her children after school, but she still needs to pick them up in the evening, meaning that she has been hitting the increased congestion in Streatham traffic four times a day.

It's been impossible, she says, and the traffic has made her so late for work that she has been put on "monitoring", so that she has to sign in and out, as well as staying later at the end of her shifts to make up for lost time. "It's affecting my mental health," she says, "I'm so stressed out."

Melissa says that in several years of working at St George's, she never had any problems getting to work on time, but now she's worried that she might not be able to keep working there. "How long are the hospital going to put up with this?" she says, "is my job safe? Is it secure? You have no control over anything. It's soul-destroying, it really is."

She started leaving the house at 7.30am - to get round the schools and back to the hospital by 9.30am - but even then her children have been late into school, she says. And at the end of the day she hasn't been getting back with them until after 8pm. "The youngest is absolutely exhausted by the time we get home."

"They say that if your journey is less than three miles then you should be using public transport. It is less than three miles, but it's impossible."

She's all in favour of the "lower pollution and greener avenues" that LTN schemes promise, she says. But the effects of the Streatham Wells scheme have made any benefits hard to see. "It makes you resent the people who are pro the LTN," she says. "This is people's lives."