There are textbooks that can be used for theme based CBI classes which usually contain a variety of readings followed by vocabulary and comprehension exercises. These can then be supplemented with additional information from the Internet, newspapers and other sources. However, another approach is to use specially constructed source books which contain collections of authentic materials or simplified versions. These can be about a particular theme such as drug use or care of the elderly, or about more general topics. It's possible to create some really interesting classroom materials as long as the need for comprehensibility is not forgotten.