Complex sentence: In past years, students have developed numerous research projects that have been exceptionally successful--some of these had research papers were published, while others went on to place in many large science competitions such as the Siemens Westinghouse Science and Technology Competition.
Split into simpler sentences: In past years, students have developed numerous research projects that have been exceptionally successful. Some research papers were published, while others went on to place in many large science competitions such as the Siemens Westinghouse Science and Technology Competition.