How to pronounce 學 "shwehh", "shoo-ehh", or "xüüehh"? According to pinyin pronunciation guides, 學 should be pronounced  x + ü + e with a rising tone. This should verbally sound something like 


  1) a shh- with tip of tongue close to your bottom teeth and gums; 
  
  2) an umlaut-sounding uuu as in the French/German 'tu' which is "xu" in pinyin; 
  
  3) an -ehh sound e.g. in 'better' or 'jet'. 


Basically, 學 is "x" + "üe". In this post, I label this standard pronunciation as "xüüehh" (with a 2nd tone). 

However, I've noticed that occasionally in regular speech:


The umlaut is glided over to the point that "xüüehh" sometimes sounds like "shwehh" (which is similar to the "shwehh" sound in the soda brand "Schweppes"). 
The -ü sound sometimes becomes a regular pinyin -u (not umlaut-ed) which consequently sounds like "shoo-ehh". This is particularly the case in common words such as 學生，學習，學校，大學 ，等等


Are these differences in pronunciation negligible? That is to say, do the differences in sound among "xüüehh", "shwehh", and "shoo-ehh" really matter in day-to-day speech? I hear the differences with a few native speakers but also fall victim myself to pronouncing 學 in these (improper?) ways, which partly motivated this post. 

Is this somewhat similar to English-speakers saying "where ya goin" instead of fully enunciating each syllable as in "where are you going"?
I must say that the differences are not negligible to Chinese people, because they won't have a &quot;sh&quot; followed by &quot;w&quot;, and that's not the same problem as &quot;where ya goin&quot;.
To your first problem, I think it's because you're still not skilled enough to pronounce &quot;x&quot; (because this consonant is absent in English, French, and many European languages, and people often use &quot;sh&quot; to replace it). If you really feel hard to go this way, choose &quot;sy&quot; or &quot;xi&quot; instead of &quot;sh&quot;, like &quot;sy-ü-ehh&quot;, and slowly progress towards the correct &quot;xue&quot; (note that in Pinyin orthography, the umlaut is omitted).
EDIT: I answered this question based almost on instinct at that time. I'll explain more about it now.
Modern Mandarin pronunciation was finally set during early 1910s with one last big change: the &quot;merge&quot; of jianyin (lit. &quot;sharp consonant&quot;) and tuanyin (lit. &quot;round consonant&quot;). Since then, consonant /z/, /c/ and /s/ cannot be followed by /i/ or /ü/, only their counterpart /j/, /q/ and /x/ can (e.g. /sing/ and /xing/ were different before this change, but then they merged into /xing/. Note that this merge does not apply to some topolects). Therefore, it is much easier for learners to imitate /xi/ or /xü/ from /sy/ or /sü/ instead of /shy/ and /shü/. You just need to lift the middle of your tongue to the upper gum from /s/ to pronounce it.