The paint in the stairwell of my home is peeling .I believe that the problem was latex over oil. In some places large flakes about 3 inches in diameter are peeling off you can scratch it off with a thumbnail .Do I have to scrape the whole wall clean or can I scrape only the peeling areas and sand the rest?

Sounds like Latex over oil.

First clean the surface with a mix of TSP (Tr-sodium phosphate).

Scraping drywall will be a real pain, but you do need to scrape anything that will come off. Lightly sanding with a course paper should expose the areas.

You can fix using redi-patch, available at Home Depot.

Vacuum the wall and then use TSP and water again. Dry with a cloth.

Imperfections will be hard to see. Use a flashlight on the edge in a dark room

drewferu, you have 2 ;osts back to back, is this the same surface in both posts. Wall or stair threads?

It is the walls I'm putting tile on the stairs