Background: Impact of a classroom-based, standardized intervention to address limited vegetable consumption of fourth graders was assessed. Methods: A 4-lesson, vegetable-focused intervention, revised from extant materials was repurposed for Pennsylvania fourth graders with lessons aligned with state academic standards. A reliability-tested survey was modified, then examined for face and content validity and test-retest reliability. Lessons and evaluation materials were modified through an iterative testing process with educator feedback. A nonequivalent control group design was stratified by local Supplemental Nutrition Assistance Program Education (SNAP-Ed) partnering organizations with random assignment of participating elementary schools as control (N = 68) or intervention (N = 72) treatments. Independent t-tests compared control and intervention group changes. A mixed effects model was created to account for classroom effects from the nested sampling method of selecting classrooms within SNAP-Ed partnering organizations. General linear model univariate analyses of variance were conducted to assess intervention effects considering gender, and food preparation/cooking experience. Results: During a 3- to 5-week time frame, 57 intervention classrooms (N = 1047 students) and 51 control classrooms (N = 890) completed pre- and post-testing. Intervention students improved in vegetable-related attitude, self-efficacy, preference, and knowledge scores (p less than 0.001). For example, intervention vegetable preference increased 1.56 plus or minus 5.80 points; control group mean increase was only 0.08 plus or minus 4.82 points. Group differences in score changes were not affected by gender or interactions between gender and food preparation/cooking experience with family. Conclusions: A defined intervention delivered in a SNAP-Ed setting can positively impact mediators associated with vegetable intake for fourth-grade students. (Contains 4 tables and 1 figure.)