As a beginner of Japanese, I very often I don't understand or completely misunderstand spoken Japanese - even if I know every word in the sentence, and may have recognized it in different context. Here is an example where I was completely stunned - had no clue what it said until I saw the text. A native Japanese speaker saying the following sentence:

まだ学校へ行くには早い時間です。
It's still to early to go to school.

(This is from some flashcard stack in Anki. The accompanying picture shows two young kids who may have just woken up.)

When listening to this first, even repeatedly, without knowing the text or any other hint, I heard roughly the following, if I had to write it down in kana:

まだが　こへい　くには　はやい　じかん　です。

Or in letters (deliberately not exactly rōmaji):

Madaga kowei kuniwa hayai jikan des

First, one thing seems to be a general rule: In 学校 the individual readings がく＋こう get contracted to がっこう. (Is there indeed a rule behind this? I heard the short pause in gakkou as a word boundary.)

The other thing I got totally wrong was the place where there are essentially four vowels in a row in 学校へ行く：

がっこうへいく in the underlined ouei. (the へ is basically just the vowel e in this situation)

I don't know exactly how to pose this as a question. But I still wonder how I can accelerate my listening understanding (besides just more training)?