Discussion and group based activities are difficult to fit into each of the different subjects in school. Here is a subject by subject analysis of how I think discussions can be incorporated in.
English: This is the easiest because most english classes already include some kind of discussion at one point or another. Discussions are particularly effective while reading a book for class so that each student can understand the subject material and ask questions about confusing parts.
Math: This is the hardest class to have any kind of discussion in and is the class you are most likely going to spend the period taking notes. To bring a group aspect to the class, perhaps students could get into note-taking groups and have each person focus on a part of the lesson. Then at the end of class each person could share what they learned.
Science: Again like math, science classes require a lot of note taking as there is a lot of information to be learned. My suggestion is for science classes to have interactive activities when possible. Having even more labs would help to keep kids interested as they usually get to move around and interact with others.
Social Studies: Another class where note taking is seemingly neccesary. However in history classes more then any other, reading a text book and taking notes is essential. I feel that instead of assigning notes as homework every night, students should instead be assigned to skim the section over and then discuss the readings the next class with fellow students so that everyone in the class has a similar understanding of the topic.