國家語委普通話水平測試? Which school to study for it is good?

我以過來人的身分回答你吧!
想學好語言一定要單對單學習,因為老師可以立即糾正發音、語法、語感、方言等問題,雖然價錢比較貴,但效果一定很好.一班同學學習時,老師也可能會叫同學一個一個的唸,不過我相信不會每一節課都會這樣做,就算有,也不會那麼細心糾正錯音,因為學生太多了.

註:一定要找北方老師

if you are a beginner, I suggest that you join the putonghua class offerred by Spare Study Centre 工聯會普通話班, 主要是學漢語拼音, because the fee is reasonable. Others are fairly high. If they offer exam course for PSC(普通話水平測試), you may then go with them. If not, when you reach certain level (having acquainted with PINYIN), you may join the intensive course from Hong Kong U, mainly for PSC.

我是普通話老師，考試也考得很好，在香港的這個考試，我幾乎拿了滿分，我可以替你耐心補習

供你參考:
http://putonghua.name