The Lambda Calculator is an interactive, graphical application to help students of natural language semantics practice derivations in the typed lambda calculus. It is designed for both students and teachers, with modules for online classroom instruction, graded homework assignments, and self-guided practice. The primary function is to assist in the computation of natural language denotations up a syntactic tree in the style of Heim & Kratzer's Semantics in Generative Grammar. To this end, the program detects common errors and attempts to provide intelligent feedback to the student user and a record of performance for the instructor.