During his professional employment, beginning in 1968 at IBM Research, Dr. Castro made it his avocation to mentor youth from underrepresented groups to advance their education in science and engineering. In 1971, he began an on-the-job training program to assist minority students in becoming technicians at IBM Research. Dr. Castro also created research positions for undergraduate students and over the next two decades hired and mentored over twenty minority and female science and engineering students. During this time, Dr. Castro frequently volunteered his time to visit elementary schools, high schools and universities to speak to students about careers in science and engineering. As President of the Society for Advancement of Chicanos and Native Americans in Science (SACNAS), Dr. Castro helped build this organization into one of national prominence that serves over a thousand students a year.