Background: Continuous calls for reform in science education emphasize the need to provide science experiences in lower-division courses to improve the retention of STEM majors and to develop science literacy and STEM skills for all students. Open or authentic inquiry and undergraduate research are effective science experiences leading to multiple gains in student learning and development. Most inquiry-based learning activities, however, are implemented in laboratory classes and the majority of them are guided inquiries. Although course-based undergraduate research experiences have significantly expanded the reach of the traditional apprentice approach, it is still challenging to provide research experiences to nonmajors and in large introductory courses. We examined student learning through a web-based authentic inquiry project implemented in a high-enrollment introductory ecology course for over a decade. Results: Results from 10 years of student self-assessment of learning showed that the authentic inquiry experiences were consistently associated with significant gains in self-perception of interest and understanding and skills of the scientific process for all students--both majors and nonmajors, both lower- and upper-division students, both women and men, and both URM and non-URM students. Student performance in evaluating the quality of an inquiry report, before and after the inquiry project, also showed significant learning gains for all students. The authentic inquiry experiences proved highly effective for lower-division students, nonmajors, and women and URM students, whose learning gains were similar to or greater than those of their counterparts. The authentic inquiry experiences were particularly helpful to students who were less prepared with regard to the ability to evaluate a scientific report and narrowed the performance gap. Conclusions: These findings suggest that authentic inquiry experiences can serve as an effective approach for engaging students in high-enrollment, introductory science courses. They can facilitate development of science literacy and STEM skills of all students, skills that are critical to students' personal and professional success and to informed engagement in civic life.