Classroom teaching has long been and still is largely an oral phenomenon, involving lecture, question and answer, group discussion, or activities like observation and experimentation. Today audio and video recording provide a powerful way of recording a class, but even video cannot capture what an individual student experiences, such as an opportunity to doodle (as in this law school class in 1868-69). Before modern recording devices and still today notes taken by students offer unique insight into the classroom experience, although notes are surely never a complete record of everything that was said.
Before printing students first had to procure a copy of the text to be discussed in class. In 13th century Paris so many students needed to copy the same original that stationers set up an ingenious system of renting out installments of the assigned text so that multiple students could be engaged at the same time in the time-consuming process of copying (or having a copy made) from a single exemplar. A manuscript at Houghton bears notes that indicate it was copied in this way, by peciation. Three hundred years later Paris students would instead purchase the assigned text in a printed versions with extra wide margins. The student would then fill the margins and interleaved blank pages with full text notes recording the commentary of the master, likely under dictation. But a full century later students at Harvard copied their textbook from a manuscript exemplar. There were so few students in each class that printing wasn't a good option; besides, the act of copying was thought to aid in retention.
Unlike these early notes transmitted by dictation or copying, modern note-taking typically involves each student choosing what to record, often in partial sentences or bullet points, as in William James's notes from his medical school days or Harvey Cushing's notes on an anatomy lecture or Henry Edwards Scott's notes on Fine Arts 5n, 1922-23. These notes also included images; did Cushing draw from a dissection in front of him, or from an image on a blackboard or other support? The student from 16th century Paris used red ink to highlight headings; when did Cushing use red? To draw veins and arteries, but also to make additions to notes first taken in blue? Note-taking is often a layered process, involving multiple stages of reading, writing, and thinking which are hard to disentangle exactly. Recommendations about how best to take notes have varied over time and by context, when they are recorded at all; for some current advice see http://bookhistory.harvard.edu/takenote/node/90
Students also took notes outside class, on their reading. Commonplace books, in which one copied interesting excerpts under headings to facilitate later retrieval, were often kept in college. Some served their owners for years afterward, as they added new material and annotated existing entries. For example, Samuel Locke continued to use his commonplace book for 22 years after he started it as a Harvard undergraduate, and George Ripley for 18 years.
Inevitably, the vast majority of student notes do not survive. Their preservation depends on the happy coincidence of actions taken to preserve them (by the note-taker, his or her heirs, and often a library or similar institution) and the avoidance of destructive forces, from fire and flood to dispersal. Thomas Crafts' 1782 notes on physics are stored in a sheet used for mathematical exercises, the context of which can no longer be identified. Why did he sacrifice some student work to help preserve his notes from that class?