Time to make waves: Ellie Simmonds - The pool prodigy with a point to prove

She won gold in Beijing aged only 13. But now she faces the US team's rising star

At the Olympics, Britain's Beijing generation didn't have much luck in the pool. None of the athletes who won gold four years ago managed to replicate that success in London. Tonight, Ellie Simmonds will set out to prove that the Paralympians won't suffer from a similarly sinking feeling.

The hex has already been broken – Britain's second gold of the Games came from Jonathan Fox, who gave the Aquatics Centre's officials reason to dig out the host nation's anthem.

But for Simmonds, the pressure is still high. The Walsall swimmer became a national sensation when, at the age of only 13, she stormed to victory in the S6 100m freestyle and later won the 400m at the Chinese games.

In the intervening four years, the expectation was to win more medals at London 2012. But the weight on her shoulders has increased dramatically given the difficulty her Beijing peers have had in keeping up their previous form at the Aquatics Centre.

It's a daunting task for someone who, even though she is now competing in her second Paralympics, is still only 17. But Simmonds, who was born with a form of dwarfism, insists the lessons learned along the way will prove invaluable when she steps out for her first race – the S6 400m freestyle – later this evening.

"I'm experienced and I know what's best," she said before the Games. "I've been with my coach a long time so he knows what's best for me. I'm very prepared, not just physically but mentally."

The hill she has to climb has also become that much steeper thanks to the arrival on the scene of an American prodigy who has created one of the Paralympic Games' most intriguing rivalries.

Victoria Arlen, 17, below, an up-and-coming champion who learned to swim again after she was left partially paralysed by a rare viral infection, smashed both of Simmonds' world records at the US trials earlier this summer, making her a hot favourite to take gold.

Simmonds is unfazed. "It's given me a bit of a buzz really, a bit of determination," she told the BBC. "I'm a very competitive person and being behind the blocks, knowing that she is the world record holder and that I have to bear her, is really exciting."

The rivalry has become even fiercer after allegations the New Hampshire swimmer has been competing in a class below her ability, potentially giving her a crucial advantage. She is one of three American swimmers who have been reclassified by sporting officials in a move which has caused significant upset among Team USA athletes.

Arlen was effectively disqualified and ruled "not eligible" to compete but a last-minute appeal has put that decision on hold pending further classification tests.

However, in a bizarre twist the International Paralympic Committee has insisted that Arlen's class allocation "is subject to any modification that may be made following observation in competition".

That could lead to an unwanted scenario where, if she swims too quickly she might end up convincing judges that she should have been competing in a higher ability category. She could effectively win and then find herself stripped of her medal at a later date.

The last-minute reclassifications – which are not unusual in a major international competition – have caused a deep unease in the American camp.

US swimming star Mallory Weggeman, who was moved on Monday from nine S7 events to the less impaired S8 category, has hit out at officials saying she felt "as though the system has failed me".

"I'm a T10 complete paraplegic," she said in statement. "I have no feeling or movement from my belly button down and I'm competing against people who are bi-lateral double amputees below the knee, who have, from below the knee up, full function."

But yesterday she struck a defiant note, insisting she would bounce back. "I see this as a new opportunity to demonstrate that when life and people knock you down, each and every one of us still has the ability to overcome and rise to the occasion.''