This article describes a STARTALK intensive summer high school Mandarin language and culture program that was conducted for three summers. Participants across the three years included 40 Mandarin Level II and 53 Mandarin Level III high school students. Quantitative and qualitative data are presented to show the effectiveness of the program. Students' language proficiency scores showed significant improvement between pre- and posttests for listening, speaking, reading, and writing. Interview and observational data are also discussed to show students' improvement in all four Mandarin language skills, as well as their increased knowledge of Chinese culture. A detailed program description including program goals, curriculum, instruction, and assessment is also shared for those who are interested in replicating the program model.