Data from a recent study show that investing in science teachers' professional growth and teaching ability is a wise choice. However, the professional development must have the right content (the science discipline that teachers are actually teaching), at the right time (when they are assigned to teach that science discipline), and in a stable environment (with teachers consistently assigned the same science discipline and continue on as teachers). As millions of dollars are invested in professional development, we cannot afford to overlook these broader truths that will ultimately determine whether students realize a return on that investment.