Should you continue contributing to a 529 plan when a student is in college?

If the student has financed part or all of college with a loan that doesn't accrue interest until after they graduate, such as a Perkins or subsidized Stafford Loan, and you have a reasonable expectation that the 529 will continue to grow tax free and/or you are getting a tax benefit, then yes. At graduation, the student will apply those funds to the loan. Granted, we aren't talking about large gains here and there are a lot of "ifs" in this answer.