Abstract Objectives Quality Diets for Better Health (QDBH) is a nutrition-sensitive agriculture project in southern Ethiopia that promotes vitamin A-rich orange-fleshed sweetpotato (OFSP) and community-based nutrition education to improve the quality of young child diets. The objective of this research is to examine the impact of the project and other predictors on caregiver knowledge of infant and young child feeding (IYCF) over time. Methods Communities were randomized to a control group and intervention groups receiving OFSP planting materials and community-based nutrition education. Households with infants <6 months completed a baseline survey in January 2018, and follow-up surveys 7 and 13 months later. Knowledge of IYCF recommendations and vitamin A was assessed at each visit; a knowledge score (range 0–100) was calculated by assigning points for accurate responses. If a caregiver was missing not more than two responses, we imputed her score with the community-mean to retain sample size and minimize bias. We used mixed effects modeling to examine the effect of QDBH and other factors, such as education and prenatal counseling, on knowledge scores over time, while controlling for covariates. Results Of the 605 households who completed the baseline survey, 548 (90.6%) and 523 (86.4%) completed the follow-up surveys. Baseline characteristics of the group lost to follow-up did not differ from those retained in the sample. Knowledge scores were highest at baseline (65.3 ± 14.4), and lower at 7 months (48.4 ± 13.8) and 13 months follow-up (46.9 ± 14.0). Baseline scores were higher among caregivers with higher education (P < 0.05) and who reported receiving prenatal IYCF counseling (P < 0.0001), but also declined faster among those who had prenatal counseling (β = −1.6, P = 0.04). Knowledge scores in intervention and control groups were similar at baseline (P = 0.49), but scores of those in the intervention group declined less rapidly than those in the control group (β = 4.0, P < 0.0001). Conclusions Caregivers’ knowledge of IYCF decreased in the postnatal period; decreases were fastest among those who received prenatal IYCF counseling and among those in the control group. Postnatal community-based nutrition education can help maintain knowledge of IYCF recommendations. Funding Sources This research is funded by the European Union in partnership with the International Potato Center.