Pilot studies of an NSF-funded project called The Math You Need When You Need It (TMYN; http://serc.carleton.edu/mathyouneed) reveal that online, asynchronous learning modules are effective at remediating students' quantitative skills in introductory geoscience in both community college and university settings. TMYN uses a just-in-time and necessity approach to mathematical learning, with online modular tutorials assigned prior to students encountering a quantitative concept in a geoscience context. Pre- and posttest scores show that TMYN modules used in conjunction with a geoscience course successfully increase student's quantitative skills. Survey responses indicate that students perceive the modules as helpful. Variation in student completion rates across the pilots illustrates challenges to effective implementation of online learning modules and suggests that instructional methods and students' perceptions (and instructor reinforcement) of task value and expectancy of success may influence student interaction with TMYN and, thus, effective mathematics remediation. Class size and focus, concepts covered, and grading stakes seem to have a negligible influence on student completion and success rates, illustrating TMYN's flexibility in a variety of instructional settings. The modular, asynchronous, and online approach of TMYN represents a promising solution to the challenge of teaching quantitative material that is contextually framed in a science context. (Contains 2 tables and 1 figure.)