Background of this study:
In Japan, training programs in which in-service teachers observe each other's classes and discuss their teaching (so-called "Lesson Study") have taken root.
However, Lesson Study (LS) in junior high and high schools has the following problems. Compared to elementary schools, where one teacher is basically in charge of all subjects, junior high schools and high schools with a subject-teacher system have a limited number of teachers in charge of the same subject within the school, making it difficult to discuss a variety of opinions during the LS sessions.

The number of teachers assigned to each subject in each school's middle and high schools varies depending on the subject and the number of students. Schools with small numbers of students often have only one or two teachers in charge of a particular subject. This is especially true for subjects that do not require much class time, such as foreign languages and music.

Inevitably, it is difficult for a sufficient number of teachers of the same subject to come together for LS in a school with few teachers of the same subject. Additionally, even if a subject has a larger number of teachers, their numbers are smaller than those of elementary schools, so only small-group classroom studies are possible.

If it is difficult to conduct LS within the school, a possible solution would be to have teachers from several junior high schools and high schools gather together for LS. In reality, however, there is another problem to be solved: the time and financial burden of traveling to the venue.

However, an opportunity (change) came to Japan several years ago that could solve this problem. In Japan, each child in compulsory education (elementary and junior high school) will be provided with one information device (e.g., tablet PC) by the national education budget starting in 2020, and all students now own a device. At the same time, all school classrooms have been equipped with wireless Internet access. Both teachers and students can now access the Internet wirelessly anywhere in the school using their own dedicated devices.

This innovation has made it possible to conduct "lesson observation" and "discussion," which are essential for conducting LS, online without having to gather at the same venue. In other words, for teachers at junior high and high schools, "barriers (cost issues)" to implementing LS have been eliminated.

However, the following issues should be carefully considered when implementing On-line “Lesson Study”(OLS). First, how to overcome the information leakage and privacy concerns that arise from sharing student activities in the classroom via the Internet in order to conduct OLS? Second, what are the criteria for effective OLS? Third, will OLS be as effective (or even more effective) than face-to-face training?

Conclusion:
So far, the following conclusions have been reached.
- The OLS not only helped overcome the costly aspects of time and money required for face-to-face LS, but also brought depth and diversity to the LS itself.
- In order to dispel concerns about privacy and information leakage, it is important to
- handle photographs and videos taken in class only within the system dedicated to teacher training (including OLS).
- state students and their parents/guardians the purpose of use, the range of viewers, and the management of collected information, and obtain the consent of students and their parents.

Keywords: Lesson Study, in-service teacher training, education, professional development.