Sometimes the words 发蒙 and 上学 can be seen together as a single phrase: 发蒙上学.
Working with the topolectical words 穿牛鼻子
one defintion says:
喻指小孩到学校读书
while another says:
比喻儿童发蒙
Is there any, fundamental, difference between 发蒙 and 上学 for children?
Or is this just more of a countryside (乡下) vs. urban idea?
This ifeng article says:
自古以来，孩子上学叫“发蒙”，早期教育叫“蒙学”。从文字角度，“蒙”这个字最早的含义，本身就与幼童启蒙有关。
It's not super clear if it is exactly the same or if there are subtle differences.
发蒙 is not used constantly in Chinese anymore.
上学 means receive education in a general way.
if you want to say education at an early age, maybe "启蒙教育" fits better.
上学is more easily understood by modern people while 发蒙 now means more "at a loss" than its original meaning to the public, but if you say 启蒙, more people will understand you.
蒙 has several meanings and one of them is “ignorance”. So 启蒙/发蒙/开蒙 （啟蒙/發蒙/開蒙） mean “enlightening”.
In my opinion, 蒙 is the imagery of covering (of course it has this meaning). The verb ahead of 蒙 (启蒙/发蒙/开蒙) corresponds to “dis-” so that you can think it as “discovering”.
(I would chosen this translation if I were the first generation of translators.)
蒙学 specially indicates the early education of children at the old time which must not be done at school, to teach at home is okay, too.
So this is not more of a countryside vs. urban idea. We just, rarely, use 发蒙/开蒙/蒙学 in popular education nowadays but use 启蒙 frequently.
启蒙 does not indicate the early age only at all, it also fits the first time on a lesson. 启蒙老师 is the first teacher on any lesson whatever age you are.
