This study aimed to further understanding of immersion language development by examining in-class freewriting, classroom-assessed reading, and year-end STAMP 4Se proficiency levels in 4th-grade Chinese immersion over an academic year. Specifically, we aimed to understand (1) how learners express themselves in freewriting, (2) growth in freewriting and Chinese reading levels across the year, and (3) relations between classroom-based measures and proficiency measured by year-end standardized tests of Chinese (STAMP 4Se). In freewriting, students used combinations of Chinese characters, Pinyin, homophones, English, and pictures. Writing and reading levels grew over the year, though the range was wide. Student reading levels measured by teachers were the most important predictor of year-end proficiency across the four STAMP 4Se domains, while freewriting predicted reading and writing proficiency. Students who engaged in digital texting activities demonstrated higher speaking proficiency. Pedagogical recommendations include incorporating freewriting, extensive reading, and digital texting to improve partner language proficiency.