The PhET Interactive Simulations project impacts classrooms around the world through over 130 interactive science and mathematics simulations (sims) and associated teacher resources. Here, we focus on our work to increase the accessibility of PhET sims to support diverse students (including students with disabilities) with features such as sonification. With our collaborators at the Inclusive Design Research Centre at OCAD University, we have overcome technical challenges, started an accessible simulation design community, developed prototypes of accessible PhET simulations, and conducted investigations into the design and use of accessibility features. This work is expanding the ways students can learn from sims, and has the potential to transform the development and use of STEM learning resources to create more inclusive classrooms. To learn more, visit http://phet.colorado.edu/en/accessibility.