The relationship between scores on scientific knowledge and scientific reasoning among 67 elementary school students in Grades 6 to 8 was investigated. Scientific knowledge was assessed by an objective test of life science knowledge consisting of 40 multiple-choice items. Scientific reasoning was assessed by a test of life science reasoning skills consisting of 10 essay items. Both scientific knowledge and scientific reasoning increased across grades and were significantly correlated. However, when controlling for scientific knowledge, grade differences in scientific reasoning were nonsignificant, but differences in scientific reasoning between boys and girls were significant, with girls scoring higher than boys.