The effectiveness of outdoor education in comparison to classroom (indoor) education and the acceptance of biology apps by students is still largely unknown. To bridge this gap, a quasi-experiment was performed with secondary school students within each of the schools. Students used a digital dichotomous key to identify woody species. One school performed outdoor identification and the other indoor identification. The students completed a pre-test and post-test on botanical knowledge, and they completed questionnaires about their attitudes toward the key and their attitudes toward biology and learning. The identification of plants with the app proved to be successful in promoting learning regardless of the learning scenario. The comparable results of the indoor and outdoor tasks indicate that the app itself is effective for learning about plants. There were no significant gender-related differences in knowledge results and opinions about the usefulness of biological keys. The key was very well accepted by students and it has proven to be an effective, interesting, and convenient learning tool for identifying organisms that allows experiential learning and learning about biology during the identification process. Published in Nat. Sci. Educ. 46 (2017) doi:10.4195/nse2016.11.0032 Received 19 Nov. 2016 Accepted 12 Jan. 2017 Copyright © 2017 by the American Society of Agronomy 5585 Guilford Road, Madison, WI 53711 USA All rights reserved core ideas • The digital identification key proved to be successful in promoting learning, regardless of the learning scenario.• Students who gained better results on the tests also had a better opinion about the app and its usefulness for learning about organisms.• No major gender-related differences were found in attitudes toward the use of this app and in knowledge.