Estimating reliability for single-item motivational measures presents challenges, particularly when constructs are anticipated to vary across time (e.g., effort, self-efficacy, emotions). We explored an innovative approach for estimating reliability of single-item motivational measures by defining reliability as consistency of interpreting the meaning of items. We applied a psychometric approach to identifying meaning systems from distances between items and operationalized meaning systems as the ordinally-ranked participant's responses to the items. We investigated the feasibility of this approach among 193 Introduction to Biology undergraduate participant responses to five single items assessing motivational constructs collected through thirteen weekly questionnaires. Partitioning among medoids (PAM) analysis was used to identify an optimal solution from which systems of meaning (SOM) were identified by the investigator. Transitions from SOM to SOM were tracked across time for each individual in the sample, and consistency groupings based on the percentage of consecutively repeated SOMs were computed for each individual. Results suggested that from an optimal eight-cluster solution, six SOMs emerged. While moderate transitions from SOM to SOM occurred, a small minority of participants consecutively repeated the same SOM across time and were placed in high consistency group; participants with moderate and low percentages were placed in lower consistency groups, accordingly. These results provide preliminary evidence in support of the approach, particularly for those highly consistent participants whose reliability might be misrepresented by conventional single-item reliability methods. Implications of the proposed approach and propositions for future research are included. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]