School business leaders need near-psychic powers. Gazing into our crystal balls, we add up the predicted income and match it against expenditure; the gap between the two indicates how viable our school business is.

But as national funding has decreased, our predictions are looking bleaker. To combat this, we use curriculum-led financial-planning tools to ensure staff deployment is as tight as possible, and carry out strengths, weaknesses, opportunities and threats analyses, looking at factors that might affect our schools in the longer term, from changing demographics to leadership succession. Yet, the one thing that most of us have not considered is the effect of current funding cuts on future outcomes.

Our strategic plans are based on the assumption that we will be able to deliver our core business of education at a “good or better” standard. But what happens when we can’t do this any more? There is a myth that, as funding pressures have increased, school standards haven’t fallen. It may be true that outcomes for those students leaving school in 2018, who have enjoyed up to 12 years of fairly funded state education, have shown no decline. However, the real effect of funding cuts will be felt by those young people who are starting school now.

As schools make tough choices and tighten their belts, teacher workload increases and wellbeing diminishes. We are already facing a recruitment crisis, but the year-on-year effects of a shoestring education system have yet to be unleashed. As GCSE and A-level subjects are cut, students are forced into taking second- or third-choice subjects, in larger classes, taught by overworked, disenchanted staff. How can that not have a detrimental effect on outcomes?

For a child who entered Year 7 this year, prospects are even worse. Schools have, rightly, prioritised the exam years, which means that any necessary reductions have been made to key stage 3. Not only is that Year 7 child now experiencing larger class sizes but they’re being taught core subjects by non-specialists, too - and the teaching assistants who might have supported them have already been made redundant. Ofsted won’t accept “lack of funding” as an excuse for declining standards.

So, as school and business leaders reviewing our forthcoming five-year growth and marketing plans, do we now need to find a methodology to factor in our own inability to deliver? If schools were truly businesses, we would be showing our shareholders a rapidly falling growth chart. The bitter irony for education is that our shareholders are the very same people who are withdrawing their investments - and that makes no business sense at all.

Hilary Goldsmith is director of finance and operations at a large secondary school. She tweets @sbl365