Eight years ago, when Laura realised that her second son was not only suffering from similar problems to her first, but that his condition was worse, a consultant asked her if she'd like therapy for herself. It hadn't occurred to her that she might be depressed about her kids. And she wasn't. Certainly, things were going to be hard. She wouldn't have rushed into another pregnancy if she'd had an inkling of the risks. But the idea of regretting Alastair was inconceivable. As for herself, Laura knew she was strong.

Her children form a hierarchy of siblings who descend in age and ability from an exceptionally bright and talented 15-year-old daughter, Shona; to Jamie, aged 12, who has adapted promisingly to some speech and learning difficulties; to Alastair, 10, who is unlikely ever wholly to adapt. Laura's experience of motherhood has been one of adjusting her hopes to very different rates of progress in her children.

In Jamie's case, it was a fight to get the help he needed. He didn't receive an exact diagnosis, though the problem was self-evident: he had some kind of speech and language disorder. His problems weren't at first deemed serious enough to merit a statement of special educational needs that would get him extra help at school. So Laura and her husband took his case to a local authority tribunal. Faced by determined parents, the council relented. Crucially, Laura insisted that Jamie's statement should include explicit provision for speech therapy.

Developmentally, he turned out to be very interesting. In year one at his London primary school, when asked to draw, the best he could manage were wobbly stick-people. But two years later, that apparent deficit had transformed into his most significant talent. One imagines neural circuits firing at varying rates. Language took longer, but with the help of speech therapy, Jamie began to catch up. Though the peer groups at his current comprehensive can be cruel, Laura senses he has an innate understanding of his difference that allows him to do his own thing without shame. He may be no great talker, but his vocabulary is unusually sophisticated. Laura says, "He's socially awkward, but considering where he was, it's remarkable."

After Alastair was born, however, it took her a long time to accept that he, too, was failing to reach the normal language markers. He missed the babbling stage, and showed even less interest in other kids than Jamie had. "I subconsciously knew," Laura says, "but I didn't want to face up to it because I'd been through all this before."

Alastair's problems proved to be even more severe. As an infant, he was hyperactive, "like Tigger, literally climbing up the walls". He got a diagnosis of attention deficit hyperactivity disorder and, by the age of six, was prescribed Ritalin. Laura feels that this has worked well for him. The idea was that, by managing his hyperactivity, the drug would allow Alastair to focus more on his language development.

By the age of eight, he was calm and lovable, but it was clear that he would not be able to manage in a mainstream secondary. In one respect, Laura feels she and her husband have been extremely fortunate. After their battle to get Jamie "statemented", there were few obstacles to his speech therapy being financed by the local education authority, and Alastair's small primary school has gone beyond the call of duty to provide him with the care and attention he needs. But despite carefully nurtured progress, he has still not acquired his older brother's self-awareness.

Yet Alastair also shows signs of having curious talents. Though he can't do maths normally, he can sometimes grasp his times tables by seeing the numbers form a pattern. He doesn't do jigsaw puzzles like other kids - working inwards from the straight edges - but rather seems to visualise complex shapes fitting together. "There's a tiny bit of me that thinks he might surprise us all and do something spectacular, because there are inklings that he's quite clever," Laura says, "though that may just be a mother's belief that her child is special."

The choice for Alastair now is between a special needs school, where the other kids would be more severely disabled than him, or an out-of-borough independent that might be more capable of developing his abilities. Laura is getting ready, once more, to battle to have his needs financed. She will not countenance the other option - of sending him away to a residential school - because she loves having him at home. "He's immature and innocent, and that's quite nice in a way," she says. "I can't force him to play with other children. I can't force him suddenly to have a huge understanding of things. I just think he's lucky that he's got a safe and loving environment."

Names and details have been changed.