This article presents the use of Physlet-based questions with proven pedagogical techniques to improve student conceptual understanding. Physlet problems are used in a Just-in-Time-Teaching approach. Most examples are from a senior level quantum mechanics class, although examples in introductory mechanics are also shown. Results of pre/post testing using the Quantum Mechanics Visualization Instrument (QMVI) show significant gain in understanding. Comparison is made with other QMVI results from undergraduate and graduate students. This article was cited as the best education article in the journal Computers in Science and Engineering for the American Institute of Physics' 75th anniversary. This citation is given below under Annotations.