Per faculty legislation, the number of a course implies its level.

The course number indicates the level of the course, with the exception of the first-year seminars, all of which are open only to first-year students and considered to be at the 100 level.

Fall and Winter offerings:
100 – 199 – Generally courses numbered 100 to 199 are introductory and open to first-year students. They do not have prerequisites.
200 – 299 – Courses numbered 200-299 are designed primarily for sophomores, juniors, and seniors, though many are also open to first-year students. If they are open to first-year students they should be so designated in the course description in the Catalog. Contact the Registrar’s office to update a course.
300 – 399 – Courses numbered 300-399 are designed for juniors and seniors.
400 – 499 – Courses at the 400 level represent specialized work for senior majors in the departments and programs.

Short Term offerings:
s10 – s29 – Generally, short term courses numbered S10 – s29 normally have no prerequisites, although they may require permission of the instructor;
s30 – s39 – Courses numbered s30 – s39 normally have prerequisites.
s40 – s49 – Courses numbers s40 – s49 are designed primarily for majors.

Independent Studies
360 is the designation for all independent studies and should be conducted at the 300-level.
s50 is the designation for independent research in Short Term.

The above information is taken from the Bates Catalog (front page of “Courses of Instruction” section) and faculty legislation.