Hi Dewanna,
Thank you for your question! Tapioca Starch/Flour is a stronger thickener so you won't need as much to replace All Purpose Flour in a pudding recipe. We would suggest using 2-3 Tablespoons of Tapioca Starch/Flour in place of the 1/2 cup of regular flour you recipe calls for. Mix the starch with some cold liquid first to make a slurry before adding into the rest of the liquid to be heated. This will help with clumping.
When a recipe called for 1/2 c flour how much tapioca flour should I use when making pudding?