You can do that with views.
The AllSections view contains all fields but no submission buttons are enabled so that it does not allow entry editing in it. In each section in the template you can add an edit button to the target section view. Use the entryactions edit pattern for designated view
You can set the section views to return after submission to the main view (in the submission settings.
As a slightly different approach you can omit the AllSections view and design all the session views to show all the fields. In each session view you can make certain fields read-only by prefixing the field pattern with !. For example (redundant spaces between brackets should be removed):
[ [!TextArea1] ]
Use the edit entry action for designated views as described above. In this approach the user will move seamlessly between views when editing sections in the entry.