When I heard that Lucy Kellaway was leaving the Financial Times to train as a teacher, I almost choked on my Cheerios. I applaud her decision to take up a position as a maths teacher in a challenging London secondary school and encourage others to do the same through Now Teach, the charity she co-founded earlier this year. But I do wonder if she has any idea what she's letting herself in for.

I spent four years teaching English in secondary schools, before retraining in journalism – the opposite route to Kellaway – and can honestly say I have never looked back. While I loved the idea of being a teacher, particularly the idea of helping young people shape their futures, the reality isn’t quite so romantic. Teaching is definitely the hardest job I’ve ever done.

As a journalist and small business owner, I work longer hours now than I ever did as a teacher. I’m often stressed and under pressure to meet deadlines. But I don’t feel constantly run-down and exhausted, like I did when I was working in the classroom – despite all the long holidays.

'Teacher asks students 'I wish my teacher knew...' and their responses are heartbreaking

In the 16 years since I left the teaching profession, I’ve often thought about why I found it so tough. I think it was the combination of a relentless workload and being on the frontline.

When I got to work in the morning, often having been up past midnight planning lessons and marking books, I had no idea what to expect. Would my beautifully planned lesson on Shakespeare's Twelfth Night be disrupted by a child throwing a chair and running around the classroom chanting "my mum’s a crack whore!" Would I find myself – a twentysomething with very little life experience – trying to counsel a girl with an eating disorder or a suicidal teenage boy in my lunch break? Would a child yell at me to "go f*** myself, whore" because I ask them to stop talking? These are all true stories, by the way – and I taught in the leafy suburbs.

Of course, the unpredictability also made the job fun. But trying to play the various different roles, including academic, administrator, social worker, counsellor, coach and mentor left me physically and emotionally exhausted; by 26, I was burnt out. Looking around the staffroom, I could see everyone else was too. They just didn’t have the energy to do anything about it.

If my friends who are still in the profession are anything to go about it, not much has changed. Teachers are still overworked, underpaid and often unappreciated. And the pressure to reach government targets, with constantly shifting goalposts, hasn’t eased up; if anything, it’s got worse.

Still, my time in the classroom has given me a healthy sense of perspective on my current work situation. Whenever I hear myself complaining about having to prepare a presentation, I give myself a good talking to. As a teacher, I had to give four or five hours’ worth of presentations every single day, then go home and prepare the same for the next – and find time for marking. I know I’ve got it easy now in comparison, and I never begrudge teachers those long holidays. They need them.

The world's toughest school run Show all 5 1 /5 The world's toughest school run The world's toughest school run Children carry their schoolbags climb on a cliff on their way home in Zhaojue county in southwest China's Sichuan province Chinatopix/AP The world's toughest school run Children carry their schoolbags accompanied by adults climb on a cliff bu using ladder as they on their way home in Zhaojue county in southwest China's Sichuan province Chinatopix/AP The world's toughest school run A child carry her schoolbag looks as she takes a rest on a cliff as she and other children on their way back to home in Zhaojue county in southwest China's Sichuan province Chinatopix/AP The world's toughest school run A village in China's mountainous west where schoolchildren must climb an 800-meter (2,625-foot)-high bamboo ladder secured to a sheer cliff face may get a set of steel stairs to improve safety Chinatopix/AP The world's toughest school run Schoolchildren carry their schoolbags climb on a cliff on their way home in Zhaojue county in southwest China's Sichuan province Chinatopix/AP

The Public Accounts Committee’s latest report, published in June, showed that the Department for Education (DfE) has “repeatedly” missed its own targets to fill teacher training places and warned of “significant shortfalls” for teachers in 14 out of 17 subjects. And according to research published by the Future Leaders Trust, Teaching Leaders and TeachFirst last week, England could be facing a shortage of up to 19,000 senior teachers by 2022.So while I don’t envy Lucy’s decision to leave journalism for the classroom, it will draw attention to growing teacher shortages. And she does have something I didn’t have – life experience – which will definitely stand her in good stead.

Although I’m sure she’s aware that the teenagers in her care won’t give a hoot whether she’s spent 22 years on the Financial Times or Doing Time, if she can’t hold their attention, they’ll be merciless. So good luck, Lucy Kellaway. I think you’re going to need it.