The 32-year-old, now the chief executive officer of the Leeds-based education charity SHINE, echoes the concerns of teachers up and down the land as she describes how their best efforts are undermined by an education system where large numbers of children fall through the cracks.
Originally from Hertfordshire, the University of Leeds economics and politics graduate got into teaching via the Teach First programme after hating the experience of a summer internship at a big corporation.
Her two placements, firstly in the Moston area of Manchester and later at Finsbury Park in the London borough of Islington, exposed her to contrasting educational challenges that sum up the ongoing North-South divide on children's attainment.
The children she taught in Jeremy Corbyn's home borough were often new to the country and living in poor, overcrowded housing, but in an ethnically diverse area many parents placed a premium on education and wanted their children to succeed.
Typically in polarised London where pockets of affluence exist next door to abject poverty, children with challenging backgrounds would on a daily basis see commuters, the Tube and the buzz associated with the vibrant capital city.
The challenges were very different in Moston, where generations of families had become used to unemployment and poor educational attainment. And for the teachers, most of whom did not live in the area, there was a sense of disconnect with the communities they served.
"We would work very hard with those children but ultimately I was driving home to my flat in Manchester city centre," Ms Spellman recalls. "So my experience was quite different than the context they were kind of growing up in."
It was during this period she realised the education of disadvantaged children would be her life's work, but could not ignore the injustice of children most in need of help being the ones who miss out.
"Our system tends to work in favour of those who already have significant advantages from home and so on where they disproportionately attend more effective schools, staffed by more high quality teachers.
"I felt that I was doing my best around that as a very hard-working maths teacher but that there were ways in which the system structurally was letting down large numbers of those children.
"There should be better ways of meeting the needs of these kids because I'm seeing this cycle of trying to offset the significant barriers that a number of these children were facing but without ever feeling like we were really addressing those barriers in specific way.
"I was teaching maths to some children for whom learning how to multiply fractions was not their most urgent need. I often felt that disconnect between what was really going on for some of these young people and what the education system was delivering for them."
Leaving teaching with no job to go to at the height of the recession in 2011, she joined SHINE, then a London-based charity supporting work with disadvantaged children in the capital and in Manchester.
It was six years later that the charity's trustees, struck by the increasing gulf between children in the capital and those in the English regions, took the bold move of leaving London and setting up in Leeds.
"We decided that actually, if we were going to be really true to our founding mission and objectives the right thing to do would be to manage a responsible exit from what we were doing in London and refocus completely on the North of England in future.
"In our sector a lot of charities have become quite risk averse. I think there's a lot of fundraising pressures that mean that London is a more lucrative place to be but actually the data shows the charity sector in terms of its resources, programmes and so on, is not well matched with the deprivation indices and overall the charities' presence in the North is much less than in London. That doesn't marry well actually with what we know about the kind of gaps and where the need is."
The North-South gap in educational outcomes is unarguable. Though the picture varies across the North, from coastal communities to big cities and smaller towns, overall northern children are finishing school with poorer grades and are less likely to go on to further education.
And Ms Spellman, who is now based full-time in Leeds and lives in the city, says the diversity of the North means it is not as simple as applying the same methods that worked in the capital.
"We take the view that often the education solutions to what children need are already out there," she says. "We really believe in the power of great teachers to come up with programmes and solutions for children.
"Some of the work we do supporting directly with teachers we find that they often know what the challenges are and they often know what the solutions are actually but what they lack often is any access to support to help get those things off the ground."
SHINE: Support and Help IN Education, was founded by a group of philanthropists in 1999 and aims to help level the educational playing field outside the capital, taking the best of its learning from London but playing to local strengths and needs.
Its focus is on three main areas – the early years, the transition from primary to secondary and backing teachers to innovate and scale up new ideas.
Amongst other projects, the charity will explore how it can help to improve on the Government’s ‘opportunity area’ programme, which was launched by the former education secretary Justine Greening in 2016 as a way of boosting “social mobility cold spots”. In total there are 12 opportunity areas, including the North Yorkshire coast, Bradford, and Doncaster.
SHINE has set an ambitious target to catalyse at least £25m into education programmes across the North by 2025 and is hoping to attract financial backing and support from guests in order to achieve this.
One of its founding members, Lord Jim O'Neill, the former Treasury Minister who helped develop the Northern Powerhouse concept, says getting education right in the North is “more important” than key infrastructure projects.
With the issue of the regional education divide now on the radars of those in power, Ms Spellman says there is now "a will to do something about it". But she says the emphasis on accountability of schools and the focus on league tables and results fail to recognise that schools in deprived areas are often fighting an uphill battle from the moment a child walks through the gates.
A child in a low-income family will hear 35 million fewer words than a child from a high income family by the time they start primary school, a fact she says public policy does not currently address.
"School is one very important input in a child's life but there's also a lot else that children bring to the school gates with them that schools then have to work very, very hard in certain areas to tackle and offset.
"One of the things we could get much better at is identifying who are the children who are likely to be the next cohort of children who struggle at school and how do we actually put in place a much more child development-oriented approach that enables us to better track and support children in each of those phases of education."
She suggests that as well as focusing on how older children find work and education opportunities as teenagers, the state, business and the voluntary sector should be focusing more on working with younger children at risk of starting school well behind their peers.
Doing so is cheaper than dealing with the consequences of a poor education when a child reaches adulthood and can have knock-on effects for families where parents do not have any qualifications.
"That's the space that I think is really ripe for investment and support but it has to start with the recognition that we're continually allowing huge numbers of these children to fail and that's not something we can actually sustain as a country."