Research and Development (Reseach and Development) is a research that develops real products through various stages of validation to determine the validity, practicality and effectiveness of these products. The purpose of this study
was to determine the validity, practicality and effectiveness of contextual-based practicum guide products as biology teaching materials on mollusca material. The
development model used in this research and development is the ADDIE model (Analysis, Design, Development, Implementation, and Evaluation). Product trials were carried out on a limited scale with research subjects consisting of 36 students in class X IPA 1 and 1 biology teacher at SMAN 1 Sendana. The validity data of the practicum guide were obtained from the results of the analysis of logical validity and face validity, the practicality data were obtained from the results of the analysis of teacher response questionnaires and student response questionnaires, while the effectiveness data were obtained from the analysis of student learning outcomes tests. The results of the analysis of the validity data of
the practicum guide show a validity level of 4.4 which is included in the valid category, while the results of the analysis of practicality data based on the teacher's response questionnaire were 96% with the very practical category and the student response questionnaire was 91.2% with the very practical category, and the results of the effectiveness analysis based on the student learning
outcomes test obtained a score of 33 (91.6%) students were declared complete and 3 (8.3%) students were declared incomplete, so it can be said that the practicum guide was very effective because it obtained the value above 80% according to the effectiveness criteria of completeness. Practicum guiding research shows that the products developed are valid, practical and effective for use as teaching materials for biology learning.