Expandable reamer assemblies include an expandable reamer module and an activation module. An outer tubular body of the activation module is rigidly coupled to a tubular body of the expandable reamer module, and an activation member of the activation module is coupled to a sleeve of the expandable reamer module, the sleeve is coupled to at least one blade and configured to move the at least one blade into an extended position. The sleeve moves axially responsive to axial movement of the activation member. Bottom-hole assemblies include an expandable reamer module and an activation module. The activation module is coupled to the expandable reamer module and configured to provide a motive force to the sleeve to move the sleeve opposite a direction of flow of drilling fluid. Methods of using expandable reamer modules include pairing two substantially identical expandable reamer modules and two respective different activation modules.