Apparently it's easy to forget how tricky learning the difference between 'b' and 'd' can be — go tutor some elementary schoolers if you don't believe me. Worse, it's only gotten harder for students given that b, d, q, and p are often the same glyph reflected across an axis in modern fonts.
3D printing to the rescue: the files attached here are models of 'b' and 'd' with arrow-shaped serifs. I've had success encouraging students to "make the arrow go with the word," i.e. aligning the arrow left to right (reading direction) puts the characters in the correct orientation.
Here's to hoping that a physical object to touch/lift will a) be helpful and b) make the process at least a little more fun.