Some words in English are quite tricky when we try to pronounce them properly. English is not a difficoult language to pronounce and has not the tricky combination of consonants as in other Indoeuropean languages, like the slavic ones. Not very often we find combinations of more than 2 consonants. However, how about this Combination existing in several english words: "SCH".
-Scheme = /skiːm/  (pronounciation in IPA)
-Schism = / ˈskɪzəm/ 
-School = /skuːl/ 
-Schooner = / ˈskuːnər /
 They all start with this combination, and the pronounciation starts with "sk".

Words like
-Schlepp = /ʃlep/ 
-Schmooze = /ʃmuːz/
-Schnitzel =  / ˈʃnɪtsəl/ 

These are foreing words that came into English and kept their original sound "ʃ" 

What about the word "Schedule? 

this word, depending on whether you are in Britain or in the US, it has different pronounciations. 

This word seems to exist since the times of middle English. It came from the french word "Cedule". As the time advances, this word retained it french pronounciation while adding other letters; meanwhile, americans tend to go through Greek pronounciation. The origine of the different pronounciations in UK and in US is not clear still, but in this blogg , there is a good explanation:

http://phonetic-blog.blogspot.com/2009/11/schedule.html

a good web page to know tha right pronounciation of the words is this one:

http://www.wordreference.com/es/translation.asp?