Olesya,
Look up ASME B36.10 and you will find all your answers. Schedule and std will match for few sizes but not necessary for all. Originally pipes were manufactured to std, XS, XXS wall thicknesses which had limited option for manufacturer/ buyer, later SCH were introduced by the ASME Committee to give a broader manufacturing/ buying options with more wall thicknesses.
Ganga D. Deka, P. Eng
Canada