Blocks-based programming environments such as Scratch are often the first experiences for young children who are learning computational thinking and programming. Unfortunately, these environments are not accessible to children who are blind or visually impaired who use screen readers, thereby excluding them from experiences that can lead to careers in STEM fields including computer science. The Blocks4All prototype programming environment makes blocks-based programming accessible on a touchscreen tablet computer. Also available with audio description: https://youtu.be/ch7CEVPCYb8