Assuming the groups and the teachers are in 2 separate entities, create an association between the two so that a teach belongs to 1 group and the group belongs to many teachers.
On the grid with the groups open a page with the edit button. This page contains a dataview of the group and within this dataview a grid/list of teachers that have a datasource over the association between the 2.
Then if you open one of the groups the list of teachers will be displayed in the grid/list.