Evidence-based knowledge about intellectual giftedness is important for identifying, counseling, and fostering intellectually gifted students. How much teachers actually know about intellectual giftedness is unclear because previous studies have relied solely on self-reports. This study aimed to: (a) develop a test for the assessment of teachers' knowledge about intellectual giftedness defined as an intellectual capacity significantly above average, the identification of giftedness, and characteristics of gifted students; and (b) inspect some correlates of teachers' performance on a knowledge test. The final version of the test comprised 38 items and a true-false-do-not-know response format. Sixty-three German secondary school teachers completed the test. On average, teachers answered 26.8% of the items correctly, 34.7% incorrectly, and 38.1% with "do not know." The higher teachers' rate of misconceptions, the more negative was their attitude toward fostering gifted students. Personal contact with the gifted was correlated with subjective knowledge but not with assessed knowledge. The results stress the importance of intellectual giftedness as a psychological topic to be addressed during teacher education.