Beijinghua is not Putonghua
Many Mandarin learners think that Beijinghua (北京话) is Putonghua (普通话), in fact, not only Putonghua, but the best Putonghua. For this reason, they seek Chinese teachers who are originally from Beijing, or they believe that they should go to Beijing to learn Putonghua.
I grew up in a small city in Hebei (河北), and Beijing is only a 30-minute drive away. As the capital of the country, the center of nearly everything, Beijing has a lot to offer. And there are always good reasons to go there. Living in a small city which did not have much at the time, I made countless trips to Beijing, class tours, family trips or friends getaways. My conclusion from my personal experience is that Beijinghua is NOT Putonghua. They are very closely related, but definitely not the same.
My empiricist conclusion is confirmed by linguistic experts on a theoretical level, that Beijinghua is really not Putonghua.
Linguistic experts say that Beijinghua was heavily influenced by Manchu language. At the beginning of the Qing Dynasty, when Manchu people who lived in Beijing were learning Chinese, their accent was influenced by their first language. And the result showed today is that Beijinghua is filled with a massive amount of neutral tone words. Moreover, just as any other dialects, Beijinghua is full of its very own colloquial and slangs which don't exist anywhere else. That implies that those colloquial and slangs probably won't be understood by people who did not grow up in the Beijing area. To put it differently, Beijinghua is a version of Chinese language integrated with some aspects of Manchu language.
In the 20th century, due to the geopolitical changes, the Chinese government started promoting Standard Mandarin (Putonghua), which is based on Beijinghua, but did not adopt Beijinghua completely. Consequently, if students have been learning standard Mandarin, Putonghua, they will find it challenging to understand Beijinghua.
It is very interesting to reflect how history has shaped a national language. In a similar scenario but much smaller scale, the same thing happened to Cantonese (广东话) and Hakka (客家话), and Shanghaihua (上海话) and Ningbohua (宁波话). It is the same reason for people who learned Cantonese find it challenging to understand Hakka, or people who learned Shanghaihua find it difficult to understand Ningbohua. I don’t really know how these local dialects have been shaped throughout the history and it is left for readers to discover.
One thing for sure is that local dialects have great influence on Putonghua teaching and learning. If students are learning Putonghua in Beijing, their Putonghua will be influenced by Beijinghua. If students are learning Putonghua in Guangzhou, their Putonghua might be affected by Cantonese. That is not to say that Beijing or Guangzhou is not a good place to learn Putonghua. On the contrary, these are great places to learn Putonghua. Indeed, students can learn Putonghua at anywhere in the world.
Learning Putonghua in an interesting place which has a lot to offer contributes to the total learning experience. That is the reason that Hong Kong makes a great place to learn Putonghua. Many students have had the time of their lives while learning Mandarin in Hong Kong.
This diversification of Putonghua can make my imagination run wild. There could be hundreds versions of Putonghua out there with slight differences from one another. Not only Putonghua with a southern accent or a northern accent, but also Putonghua with Italian accent, Thai accent or Portuguese accent! Fortunately, Putonghua, despite the influences of the local dialects, is common enough to enable people to understand each other no matter where they have learned their Putonghua, or what their mother tongue is.