I recommend Molles' text (assuming you really feel the need to use a textbook, and I probably would only use it as reference) despite the previous comment. Many EcoEd members use Molles according to a survey by the ESA education coordinator (join EcoEd if you want to chat about teaching ecology). As for why ecology should be taught before college, as a couple of other members have commented the subject is much more accessible to students than other areas of biology. Once students are excited about ecology then you can get into teaching other aspects of biology, including any fundamentals you feel students need to understand ecological phenomena, and they'll actually listen (take a look at education literature for research and theory to back this up).
Rachel Schwartz NSF GK-12 Fellow PhD candidate in Ecology University of California, Davis
