The teachers at Barnard are really some of the college's best assets. You will find that in contrast to other schools, the teaching assistants (TAs) only grade papers, proctor exams, and offer additional help on homework. This is not only true for introductory lectures, but for labs and recitations, as well. For the most part, teachers at Barnard are very accessible and will accommodate students who need extra help. Professors have been known to even give out their home phone number, if the need arises. Of course, this isn't to say that there is no variation among the teaching staff, only that the odds of getting a professor who will make time to learn your name and answer specific questions are very good. One of the major things that a prospective student should be aware of when looking into Barnard is that classes are open for cross-registration throughout Columbia University's undergraduate colleges, which means that courses may be taken at the Fu Foundation School of Engineering and Applied Science (SEAS), Columbia College, and Barnard College.
This means Barnard professors are tenured by both Barnard College and Columbia University. However, it also means you might, and almost certainly will, take a class at Columbia. The only bad thing about Barnard's affiliation with Columbia is that graduate student TAs teach all lab sections and popular courses, like "Calculus IA." But TAs aren't all bad. They are just less concerned with student welfare in their course than a full professor might be.