One of my favorite lessons when we learn about weathering is to take the students outside for about 10 minutes, with dry erase boards, to look for examples of weathering, draw it, and decide if its chemical or physical weathering. Then, of course, they have to share they findings.
Students find it very exciting. It takes some management, but can easily be done in a short class period and on school grounds, even in an urban setting. They love it! Its a big change.
Here is a link to other ideas:
this document: http://www.eric.ed.gov/ERICWebPortal/search/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=ED344732&ERICExtSearch_SearchType_0=no&accno=ED344732
which is available in full text here
Enjoy, and let me know what you do in your classes to get them out of class!