The differences between the B.A. and B.S. in math are pretty clearly stated on the Math Dept.'s website.
The B.S. route is recommended for those planning to go on to graduate level studies in math and/or are interested in scientific applications of math. The B.A. route is suggested for students interested in teaching math at the K-12 level or who want to pursue a double major or minor in a non-quantitative subject.
If you compare the B.S. and B.A. requirements directly, you'll see that the B.A. program offers more flexibility for taking electives (providing more open slots in your schedule for pursuing a double major or a minor), because the B.S. program has many more required courses.
No. of required math classes: 8 for B.S., 5 for B.A.
No. of elective math classes required: 12 credits for B.S., 18 credits for B.A.
No. of science classes required: 12 credits for B.S., none for B.A.
B.S. in Mathematics - Mathematics Department - Boston College B.A in Mathematics - Mathematics Department - Boston College
Up until 3 years ago, BC offered only the B.A. in math. Last spring, BC awarded its first B.S. degrees in math (5), in addition to 36 B.A. degrees in math. I suspect that the proportion of B.S. degrees will be significantly higher for the Class of 2012 since it was the first class to have had 3 full years to schedule and complete all of the necessary classes.