Workshops can be a powerful tool to support students as they develop proof-writing skills. In a workshop, each student writes a proof, provides feedback on other students' work, and reflects on critiques from peers. Workshops can be used in any class that emphasizes writing proofs or other forms of mathematical writing. They are highly efficient homework assignments, as workshops engage students in multiple roles: author, critic, and as the recipient of feedback. This article describes an implementation of online proof-writing workshops supporting a face-to-face class, with examples of student work and a discussion of benefits and challenges.