Purpose: This study aimed to identify the effect of using reflective diaries in 4th grade Turkish classes on bilingual students' academic achievement and writing skills. Research Methods: A one-group pretest-posttest design was employed with a study group of 4th graders identified according to convenience sampling method. Data were collected by utilizing the Academic Achievement Test for Turkish Course for measuring students' academic achievement in Turkish classes in addition to the Writing Skills Scoring Rubric for evaluating students' written work and writing skills. Both the test and the rubric were developed by the researcher. During the intervention phase of the research, students were asked to write their daily achievements in their reflective diaries for 13 months. Feedback and corrections were provided for these reflective diaries and the effect of reflective diaries on writing skills were explored. Findings: Findings revealed significant relationships between students' academic achievement and writing skills. There were no significant differences in students' academic achievement and writing skills in terms of gender. Implications for Research and Practice: Results of the research indicate that using reflective diaries increased bilingual students' academic success and improved their writing skills irrespective of gender.