NASA: What Exactly Is a Sunspot?This tutorial from NASA's Earth Observatory is a student-friendly introduction to the nature of sunspots, what they are, and how we observe sunspot activity. Short and concise, but packed with relevant information.
Phys.org: Sunspot Formation RevealedUntil a few years ago, we really had little knowledge of how sunspots are formed. This easy-to-read article from phys.org explains the groundbreaking interdisciplinary research of 2014-2015 that allowed scientists to witness the "birth" of sunspots. Read to understand their theory of how streams of magnetism in the solar interior burst onto the surface of the Sun, then self-organize into larger, planet-sized conglomerates to form a sunspot. But Wait! See entry below.
Max Planck Institute: Supercomputer Sheds Light on Sunspot FormationThere are now two competing models to explain how sunspots are formed. The Aalto University in Finland and the Max Planck Institute teamed up in 2017 to use the Mare Nostrum supercomputer to examine whether sunspots originate deep within the Sun or near the Sun's surface. The conclusion: "The (prevailing) model does not take into account turbulence." Authors of this article contend that sunspots are formed near the Sun's surface, not its interior. Teachers: Have your students read both articles. Which theory do they find to be better-supported?
ESA Cesar: General Understanding of the SunDon't have astronomy textbooks in your class? Here you'll find a well written ten-page introduction to the sun's magnetic field, structure, and sunspot cycle. Developed by the European Space Agency's CESAR project, the resource is appropriate for high school physics courses and/or community college introductory physics.
NASA Earth Observatory: The Butterfly EffectDetailed observations of sunspots show they do not appear at random over the sun's surface, but are concentrated in two latitude bands on either side of the sun's equator. This short tutorial explains this pattern, known as the "Butterfly Effect".