We report on the development of an item test bank and associated instruments based on the National Research Council (NRC) K-8 life sciences content standards. Utilizing hundreds of studies in the science education research literature on student misconceptions, we constructed 476 unique multiple-choice items that measure the degree to which test takers hold either a misconception or an accepted scientific view. Tested nationally with 30,594 students, following their study of life science, and their 353 teachers, these items reveal a range of interesting results, particularly student difficulties in mastering the NRC standards. Teachers also answered test items and demonstrated a high level of subject matter knowledge reflecting the standards of the grade level at which they teach, but exhibiting few misconceptions of their own. In addition, teachers predicted the difficulty of each item for their students and which of the wrong answers would be the most popular. Teachers were found to generally overestimate their own students' performance and to have a high level of awareness of the particular misconceptions that their students hold on the K-4 standards, but a low level of awareness of misconceptions related to the 5-8 standards.