一堂课 can be divided into several sections, each section is called 一节课. Therefore, 一节课 is a part of 一堂课 and this is commonly exists in college. Most of lesson in Chinese universities include two or three sections each week, and each section lasts around 50 minutes with 10 minutes break among them.
However, 一堂课 can also equal to 一节课 in primary schools or high schools as it does not include separate sections there.
