This study investigated the noticing of teachers who teach mathematics at different grade levels in the context of lesson study. The study specifically focused on teachers' noticing during the planning phase of the lesson. For this, the lesson planning phase of a group of four teachers consisting of kindergarten and primary school 1st grade teachers (vertical teacher team) was investigated. Teachers' planning process for the 1st grade level mathematics lesson was the focus in the context of lesson study. We examined categories and subcategories that emerged in the planning phase of the lesson study and noticing levels dealt with those categories. We examined which categories and subcategories emerged in planning and at which noticing levels they dealt with those categories. The results of the study provide comprehensive data on categories and noticing levels of teachers teaching mathematics at different grade levels in the collaborative planning process of a lesson study focusing on improving problem-solving. The results of the study showed that the teachers' noticing was clustered under three categories: curriculum, teaching methods, and conceptual understanding. In terms of noticing levels, the study's results revealed that noticing is performed at the attending to level in all categories. Although less frequently than the attending to level, teachers noticed making sense of level in all the other categories except the curriculum category. Besides, noticing that the deciding to respond level did not occur at any level might be due to the cultural challenges of adaptation of lesson study and the amount of support, we researchers provided teachers as facilitators.