Gayathri Kumar, a Year 9 pupil at Merchant Taylors' girls' school, Liverpool, clinched the title after successfully spelling words like chihuahua and troglodyte.
The week-long series, billed by the BBC as an emotional rollercoaster not for the meek, was hosted by Eamonn Holmes.
It featured clips from regional heats where 100,000 children spelled words such as curmudgeon, flummox and glockenspiel. The 50 finalists then battled it out under spotlights on a dimmed stage as newsreader Nina Hossain asked them to spell words such as meerkat, dromedary and elevenses.
Some fought back tears as they got knocked out of the contest and lost out on the prize of a holiday and pound;5,000 worth of media equipment for their schools.
Julie Brandreth, headteacher at 13-year-old Gayathri's pound;2,184-a-term school said: "We are very supportive of Gayathri's decision to take part and we are extremely proud of her. I do not know if I would have been able to spell those words under that kind of pressure.
"What I admired about Gayathri was her cool-headedness."
But, she added: "If they ran Hard Spell again and another girl wanted to participate we would talk to the parents because we now know what it involves. It is a pressured scenario and some of the children did seem upset when they were eliminated. It was like The Weakest Link. I would want parents and children to understand what they were getting into."
Media pressure meant that Gayathri and her family had decided to stop giving interviews by the time The TES went to press.
Nicholas Tucker, a former psychology professor at Sussex university and educational psychologist who works with vulnerable children in London schools, said: "Hard Spell was horrid. I did not like the way the presenter got at the kids by saying, 'You're not going to get the holiday' and the way the camera focused on those who were knocked out and struggling with tears. It was vulgar and exploitative."
A BBC spokeswoman said: "Our research showed that children between 11 and 14 like to be competitive and younger children like to work in teams. The children were very much guided through the process, and at the end of the day it was supposed to be fun.
"Obviously nobody wants to see children crying but any competition has to have its losers unfortunately. Taking part was very competitive as the standard of spelling was extremely high and the children taking part rose to the challenge and performed brilliantly."
The BBC hopes to air another series of Hard Spell next year.
Nisha Abraham-Thomas, a Year 8 pupil at Wolverhampton girls' high school, came second in the competition. The word dachshund proved her nemesis. The 12-year-old said: "I was kind of upset when I lost. My friend has a dachshund but the way the presenter pronounced it put me off. But I would definitely do it all again."
David Butler, chief executive of the National Confederation of Parent Teacher Associations said: "It was a good project that can only encourage children to be more interested in literacy. Children enjoy that kind of pressure in a funny sort of way. We all work a bit better under pressure."
Stephen Twigg, education minister, backed the programme: "Anything which helps raise the awareness of the hard work pupils put into spelling is a good thing."
Visit www.bbc.co.ukhardspell hardspell_game.shtml to play the game - minus the lights, cameras and Eamonn Holmes
* The spellings that made Gayathri a champion: Accolade reimburse insatiable elevenses nyctophobia martyr odorous triennial subpoena dromedary fierce papyrus graffiti deciduous apocalypse grammatical genealogical metamorphosis intelligent troglodyte claustrophobia geisha resuscitate disequilibrium chihuahua.
The 20 most common spelling mistakes in secondary schools, according to education and learning specialist Susan Rooney, who has taught English for 30 years: Accommodate address believe business definitely embarrass friend government jewellery library necessary niece payable possible receipt responsible rhythm secretary separate surprise.