Americans pronounce 'schedule' as 'sked-yule' but Britons prefer 'shed-yule' Both pronounce 'scheme' as 'skeem' Why do we Britons use the soft sound of 'sch' when we say 'schedule' but the hard sound for 'scheme'?
Good old Noah Webster would appear to have been responsible for the skedule form's adoption in the USA.
In Middle English, the form was usually cedule or sedule, so neither the ''h' nor the 'k' sound was present back then. From the 16th century the 'sh' appeared and has remained standard in British English ever since.
Fred suggests that Britons prefer 'shedule'. Well, they did 50 or 60 years ago, but I haven't heard anybody on British TV or radio say 'shedule' for years.