The theoretical results for the diffraction of electrons by a disk and a pair of rectangular slits is derived from the Schrödinger equation using results from time‐dependent perturbation theory in both the strong and weak scattering limits. The double‐slit ‘‘thought’’ experiment is often used in introductions to quantum mechanics as a demonstration that electrons have wave‐like properties. It seems desirable to include a derivation of the result both as an interesting example and also as reassurance that the diffraction of ‘‘matter waves’’ leads to the same results as the diffraction of electromagnetic waves by the same obstacle.