Materials developed by the Visual Quantum Mechanics project teach some basic ideas of quantum mechanics to high school and introductory college students by integrating hands-on activities and computer visualization. During field tests of the materials we obtained data concerning student understanding of some quantum concepts including potential energy diagrams, energy levels and spectra in atoms, energy bands in solids, wave functions and probability, and quantum tunneling. Data were collected from written responses of students structured interviews and a concept map. While a few misconceptions persist, the overall results indicate that students seem to have acquired a good general understanding of some important concepts that are usually not taught at the introductory level.