The Maria Mitchell Association (MMA) honors America's first professional woman astronomer who believed that students learned best by doing real research projects. The MMA is dedicated to furthering science education, encouraging women in science, and serving as a science resource for Nantucket, MA. The Association celebrates its Centennial of the Maria Mitchell Association Organization (1908-2008) and the fiftieth anniversary of its outstanding undergraduate mentoring program. The program of supervised undergraduate research was initiated by Dr. Dorrit Hoffleit, the second MMO director, in 1957, and it is currently under the guidance Dr. Vladimir Strelnitski (1997 – present). An analysis of the MMA astronomy alumni/ae career paths shows that the MMA’s mentoring principles bring remarkable and ever improving results. In particular, the percentage of MMA astronomy alumni/ae attaining the PhD level increased from the (relatively high) value of approximately 20% in the first two decades of the program to about 60% in the last decade, this probability being now approximately equal for the male and female MMA astronomy interns – a remarkable and promising achievement, given the relatively small numbers of PhD-level women researchers and professors in American astronomy and physics.