Instructional strategies for teaching concepts have long been identified. Less commonly studied is a learner's level of confidence and certitude in their knowledge based upon exposure to these instructional treatments. This experimental research study used an instrument referred to as the Spatial Probability Measure (SPM) to solicit levels of learner confidence in their knowledge base. This instrument is unique in that it has many of the characteristics of a multiple-choice assessment instrument but differentiates itself by collecting data from a continuum instead of the discrete options provided by multiple-choice. The SPM described in this article is of particular interest to designers of computer-based instructional applications because it retains much of the efficiency of the multiple-choice technique while potentially providing designers with additional useful information that can be used to inform an adaptive instructional experience. The study confirmed the validity of concept acquisition strategies described in such models as Merrill's Component Display Theory (1983), while raising additional questions and opportunities concerning the SPM instrument.