 Simson began to compete in shot put as a teenager at Thurrock Harriers in Grays, Essex.He won the junior (under-15s) category at the 1984 English Schools Championships, was the intermediate (under-17s) champion in 1986, then succeeded Simon Williams to the under-19s English Schools' title in 1987.He established himself as the top young shot putter of his generation, winning four straight titles at the AAA Junior Championships and three straight AAA Junior Indoor titles.