She represented Wales in the Commonwealth Games in Australia and won two gold medals at the International School Sports Federation championships in Athens this summer.
Julie, who learned to swim while living in Holland, is worried thousands of children are missing the chance to follow in her footsteps.
She said: "I don't think it is good enough. The results are quite bad for something that is supposed to be part of the national curriculum.If you can't swim you can get into trouble and drown. I am a lifeguard and I have seen people struggling in water."
Julie, who won the 200 and 400 metre individual medleys, was the most successful member of an England team that won four other gold, seven silver and four bronze medals. She said: "I wasn't expecting to win at all. I was relieved my hard work paid off. I didn't swim as well as I wanted to in the Commonwealth Games."
Sue Marks, head of Tormead, said: "We are thrilled Julie has achieved such success in Athens. Her dedication is an inspiration to her fellow students here."
The other gold winners at the ISF swimming championships were Jonathan Quinn in the 400m individual medley, Peter Thompson (200m Butterfly), Ellen Gandy (400m freestyle) and the men's 4x100m medley relay. Competitors from 37 countries took part in the championships which also included athletics.