1. CACAO is a program that engages undergraduates in functional gene annotation using the Gene Ontology by framing it as a teaching activity with incentives like competition and potential publications. 2. In the initial pilot, 20 students volunteered and 16 completed annotating E. coli genes on EcoliWiki in teams over 2.5 weeks with training meetings. Students enjoyed the competitive aspect. 3. Lessons learned include needing more training on finding appropriate papers for evidence and allowing more time for challenges and mentoring. The program will be expanded in Fall 2010 to recruit more participants from various institutions to annotate non-E. coli genes as well.