In order to reduce classroom overcrowding while maintaining academic standards, Omega High School last year tested an online physics course with twenty volunteers from the senior class. Although they met with the teacher once a week for lab work, the students attended all lectures and did all their homework via remote computer. All of the students in the online physics course easily passed the statewide physics exam at the end of the school year. Administrators at the high school concluded from this test that all students can learn effectively outside the classroom and decided that Omega High School should offer all of its science courses online.
Which of the following, if true, would cast the most doubt on the conclusion drawn above?