This study describes the types of food-portion tools used and changes in accuracy for food-portion size estimation by adult populations after an intervention of food-portion education and training. This systematic review searched 7 scientific databases. Only internally comparable study designs were included. Studies were tabulated for nutrition- and non-nutrition-trained university students and the general population. Included studies were assessed for level of evidence and quality, including risk of bias. Thirteen studies were reviewed, with 8 targeting university students. Food type, length of training, number of tools, and the impact of repeated use on food-portion estimation were summarized. Estimation accuracy calculations across studies were not consistent, and training was found to improve portion-size estimation accuracy in the short term (4 wk). Computer-based training tools only identified for the general population were equally or less effective and shifted estimation from under- to overestimation. This review suggests that education with food-portion tools may be effective in improving estimation skills in university-recruited participants and the general population. Computerized tools for university students are required, likely combined with other tools for improved estimation accuracy. The use of food models or multiple tools is more effective until a tailored computerized solution is developed. Repeated training is needed to maintain skills over time. This systematic review was registered with PROSPERO at http://bit.ly/2mZK3u3 as CRD42016038110.