The Shack–Hartmann wavefront sensor (SHWFS) is a standard detector used in the measurement of a light wave's wavefront shape. However, its relatively high price restricts its use as an educational tool in instructional optics laboratories. In this work, we show how a low-cost educational SHWFS can be assembled using spare parts and also provide the computational codes necessary to analyze the obtained data. We demonstrate the utility of our sensor by measuring the collimation of a beam, comparing the shape of sample spherical and cylindrical wavefronts, and demonstrating some effects of lens aberrations. We also discuss the spatial resolution and measurement uncertainties of this sensor. The experimental results are in excellent agreement with theoretical calculations. The outcomes of this work can enhance the efficiency of instructional optics laboratories and enrich the knowledge of students regarding important concepts in classical optics.