This study examined the impact of an inquiry-based instructional intervention on (a) children's ability to conduct science inquiry overall and to use specific skills in inquiry, and (b) narrowing the gaps in children's ability among demographic subgroups of students. The intervention consisted of instructional units, teacher workshops, and classroom practices. The study involved 25 third- and fourth-grade students from six elementary schools representing diverse linguistic and cultural groups. Quantitative results demonstrated that the intervention enhanced the inquiry ability of all students regardless of grade, achievement, gender, ethnicity, socioeconomic status (SES), home language, and English proficiency. Particularly, low-achieving, low-SES, and English for Speakers of Other Languages (ESOL) exited students made impressive gains. The study adds to the existing literature on designing learning environments that foster science inquiry of all elementary students.