It's interesting that you should pose these questions because I was in some first and second grade inclusion classrooms today where the teachers and I  were working on exactly these challenges. We decided to try a few new things tomorrow so I'll add what we learned afterwards. We're going to try the following:

• The teachers are planning to move in and out of the partnerships during the discussions to listen in and support as needed. They are going to try and listen to different groups during each Turn to Your Partner.
• Most of the children who are struggling are the ELL and special education students. In one of the classrooms the teacher has been partnering with a new mainstreamed student to help with the transition. Tomorrow we're going to put that student in a triad and provide support if needed. This should free the teacher up to support other students while the mainstreamed student takes on more of the responsibility for listening to others and sharing her own thinking.
• We noticed today that during the partner work and whole class discussions that some children always talked and raised their hands to share while others appeared passive. Tomorrow we're going to try to call on students who have not talked during the partner work to share what their partners said with the whole group. We're planning to let the students know ahead of time that we will be calling on different groups so they will not need to raise their hands during the class discussions. 
• We're going to work on adding new or different ideas and information during the whole class discussion to help the students go deeper with their conversations in general. Our plan is to try to limit the teacher talk after responses to simply asking for more ideas from others. The teacher is going to try simply nodding and asking "Who can add to what ______ said?" or "What do others think?"