Research on the age of learning effect on second language learners' foreign accents utilizes human judgments to determine speech production outcomes. Inferences drawn from analyses of these ratings are then used to inform theories. The present study focuses on rater differences in the age of learning effect research. Three groups of raters who differed in their native language background and language experience participated in the study: inexperienced native English speaker (NES) raters, experienced NES raters, and advanced nonnative English speaker (NNES) raters. All raters evaluated 64 speech samples taken from both NESs and NNESs who varied in their age of arrival in the second-language-speaking country. Results from the study showed that experienced NES raters were better than the other two rater groups at distinguishing NESs from NNESs. Although no rater group differences were found in scaling speakers' foreign accents or in their interrater reliability, inexperienced NES raters were stricter in their ratings than both experienced NES raters and advanced NNES raters. Implications for research on age of learning effects are discussed.