Complex sentence: The Harvard Summer School, founded in 1871, is the oldest academic summer session in the United States; that at The Colorado College is younger, but makes a distinction in that it has been continuous, whereas Harvard has not.
Split into simpler sentences: The Harvard Summer School, founded in 1871, is the oldest academic summer session in the United States. While Colorado College Summer School is younger, it makes a distinction in that it has been continuous whereas Harvard has not.