A furious dispute has erupted on Mumsnet on just how equally blended families should treat their children.
A woman has posted on the site asking for advice over school fees for her own two children and her partner's daughter.
See also: Divorcees struggle to amass any savings
Her two are privately schooled, while her partner's daughter goes to a state school - and, when they moved in together, he said he was happy with this.
Now, though, the daughter is demanding that she should go to the same fee-paying school as the other children - and that, if not, they should be removed from their school.
"I said to [my partner] 'so what did you say??!' And he said 'oh I just told her we'll look into it', she writes.
The dilemma is complicated by the fact that the partner can't possibly pay the third set of school fees himself, as he's on a very low income.
"I'm feeling like a complete mug now. He's already moving into a house which will be paid for mostly by me as his wage is so low and he has no savings so I've paid the deposit too," the woman writes.
"Am I being unreasonable to tell me I'm not paying for her schooling? And I'm certainly not taking my kids out of their school?!"
Opinion is divided amongst other posters on the site.
"If you're all moving in together surely you're going to be a family. If not what's the point?" asks one.
Another says "I do think you should aim for 'fairness' as much as possible. Having one sibling have a very different upbringing to the other two could easily end in a 'Cinderella' type situation if things aren't carefully handled.
Others, though, suggest that the girl's schooling is for her own parents to sort out.
"It would be different if you chose to put yours in private school once you were living together but why should your children be removed now because his daughter doesn't like it? Her education is the responsibility of her parents! Does your children's father contribute to their school costs?," one poster says.
Another points out that things could get more complicated down the line: "If you do decide to pay for her schooling then he needs a plan for what he'll do if you split up. He can't expect her to yo-yo in and out of schools," she writes.
In law, of course, the child's parents remain responsible for financing her, and the Mumsnet poster has no obligation to pay a penny even if she and her new partner eventually marry.
In practice, though, there are clearly potential problems with treating one child differently from the others.
Couples should talk things through and consider having a cohabitation agreement drawn up by a solicitor before taking the plunge.
What do you think about this situation? Let us know in the comments below!