Singapore is officially the country with the smartest high-school kids in the world .    The  country's academic success has helped it become a thriving economy, and  the way it has built its education system could hold lessons for the  rest of the world.   "Singapore is a fascinating case," said Marc Tucker, the president of the U.S. National Center on Education and the Economy .  "[It] was a major British port before the Second World War. When  Britain got out and closed its base Singapore was in terrible shape.   "Now today they are one of the best performing economies in the entire world. They did it largely with education and training."   If  Singapore's rags-to-riches transition was built on education, the  secret of its education system is the quality of its teachers. "They  source their teachers from among the best kids coming out of their high  schools," explained Tucker.   'Creative use of knowledge'   In  the post-war y...