Lesson study is an activity where teachers together plan, observe, analyze, and improve their learning. Lesson study is a collaborative activity of a group of teachers to: (1) plan the steps of learning, (2) one of them practices the planned learning and the others observe the learning process, (3) evaluate the implemented learning, (4) improve the original planning, (5) practice it again, (6) re-evaluate the implemented learning, and (7) share experiences and findings from the evaluation results with other teachers.

Figure 1: Sharing perceptions of mathematical literacy learning objectives

Mathematics learning is expected to significantly develop students' mathematical literacy skills. Mathematical Literacy (Numeracy) is the ability to think using mathematical concepts, procedures, facts and tools to solve everyday problems in various types of contexts that are relevant to individuals as citizens of Indonesia and citizens of the world. Mathematics teachers in the field need assistance to be able to design and implement lessons, including preparing learning tools (lesson plans and worksheets) that are oriented towards developing students' mathematical literacy skills.

Figure 2: Lesson plan discussion activity

Lecturers of Mathematics Education, FMIPA UNY, consisting of (1) Endah Retnowati, PhD; (2) Dr. Djamilah Bondan Widjajanti, M.Si.; (3) Endang Listyani, M.Si.; and (4) Husna Arifah, M.Sc. in collaboration with MGMP Mathematics SMP Kulon Progo Regency organized a mentoring activity for the Development of Mathematical Literacy Skills (Numeracy) of Junior High School Students in Lesson Study format. Mathematics lecturers and teachers collaborate in planning (plan), implementing learning (do), and conducting evaluation/reflection (see). There are five Mathematics Education students involved in the activity as assistants to the teaching team. In more detail, this activity will be carried out in the following stages.

• Equalization of perceptions about numeracy learning and lesson study steps between lecturers, teachers, and students, through online material exposure.
• Preparation of learning tools by lecturers and teachers together.
• Teaching practice by the model teacher and observation of the results (offline).
• A meeting for reflection is held after the lesson is conducted (offline).

Planning to implementation and evaluation of activities took place from July to September 2022, both online and offline. A total of forty teachers were involved in the plan phase, but only fifteen core teachers were directly involved in the do and see phases, due to limited classroom observation space. Teacher and student participants enthusiastically participated in the activity from beginning to end. From the evaluation results, it was found that lesson study activities like this need to be carried out continuously. All participants felt directly the benefits of lesson study, namely how to organize effective learning to improve student numeracy.