More than 200 middle school and high school students from underserved urban communities in Boston, Lowell, and Lawrence, Massachusetts, participated in afterschool and summer enrichment programs over a three-year period, using hands-on learning materials and web resources to complete hands-on microcontroller-based projects. Program content was based on a suite of robotics and electronics kits developed by the University of Massachusetts Lowell and Machine Science Inc., together with on-line instructions, a web-based programming tool, and a shared electronic portfolio of student projects. Participating students worked with classroom teachers and undergraduate mentors to complete a series of projects, and took part each year in a non-competitive robotics exhibition and a competitive robot sumo tournament. Goodman Research Group assessed learning outcomes and attitudinal changes using a variety of measures, including observations of program sessions, group interviews with participating students, pre-and postprogram student surveys, and educator feedback. The program was found to effectively engage participants, give them real engineering and programming skills, improve their attitudes toward science, technology, engineering, and mathematics (STEM) subjects, and increase their interest in STEM career pathways. These results are presented, along with lessons learned from the program implementation, technology development, and evaluation.