Mobile learning has been recommended for motivating students on field trips; nevertheless, owing to the complexity and the richness of the learning resources from both the real-world and the digital-world environments, information overload remains one of the major concerns. Most mobile learning designs provide feedback only for multiple choice items to guide students' learning. The aim of this study was to develop a series of worksheets as scaffolding to support inquiry-based ecology observations in a mobile learning environment. Based on a three-layer worksheet framework, a mobile learning system with in-field scoring rubrics was developed to guide the students to sequentially focus on guided observations, independent observations, and extended inquiries. Well-designed worksheets, instant feedback and supplementary materials were provided to balance the students' learning pressure and task challenge in the species-rich field. The automated scoring data for constructed response tasks were analyzed to investigate the learning growth and students' learning characteristics. The results showed that the proposed approach was effective in improving the field observation performance of the students. Furthermore, nearly 70% of the students who learned with the proposed approach could pursue their own inquiries in the mobile learning environment, showing that the approach is promising.