This study aimed to develop, pilot, and validate an aptitude test for Hungarian learners of English. A literature review on the construct and tests of aptitude is followed by two parts: a pilot phase on the development of a new aptitude test and a main study involving 419 12-year-old children in 10 schools. Data were collected on the aptitude test, English proficiency tests, and a measure of learners motivation. The article explores how aptitude scores relate to learners performances on the proficiency measure, motivation, gender, school achievements, and grades in English. The results of a multiple-regression analysis indicate that the variable of language aptitude explained over 20% of the variation in English language performance, thus proving to be the best predictor of outcomes.