This study investigated the use of a contextually sensitive instrument to assess the effect of invasive species monitoring training on the scientific literacy of citizen volunteers. The authors measured scientific literacy scores before and after 57 citizens participated in a 2-day event to learn to monitor invasive species with an instrument including 1 general-measures (Science and Engineering Indicator [SEI]) item and 4 newly developed contextual items. Ninety control subjects were also tested with a mailed survey that included the SEI item and the contextual items. Control scores, compared with trainees' pretest scores with the chi-square (SEI) and independent-samples t-test (contextual), did not differ significantly from the pretest scores of trainees on either the SEI (p = 0.68) or the contextual (p = 0.11) items. The authors compared trainees' pretest scores with their posttest scores using McNemar's chi-square (SEI) and a paired-samples t-test (contextual). Posttest scores on the SEI item were not significantly (p = 0.52) different from pretest scores. However, posttest scores on the contextual instrument were significantly (p = 0.007) higher than those on the pretest. The authors' multi-item context-sensitive instrument detected significant science literacy gains that were not detected by the single generalized SEI item. Multi-item contextual instruments may offer a promising, feasible approach for the development of new instruments to assess the effect of training in invasive species monitoring, and possibly other types of citizen science programs, on the scientific literacy of citizen scientists. (Contains 3 footnotes, 1 table, and 2 figures.)