this kind of reading in psychology is called dyslexia.
"Metacognition: Many children with Dyslexia act impulsively. More often than not, they struggle with planning in advance and thinking about their consequences."
(I should write a book about "sheet music dyslexia" ...)
Of course there are many different factors for this. Most important the reduced ability of visual perception and optical differentiation. This sometimes it is just depending of the impulsiveness mentioned above.
In our society such children are trained in special schooling to improve those lacks and often this lessons are during the music lessons! Sadly they are missing quite the right and one of the best things that would help them to compensate.
Of course the music teacher could give advice to the parents to train them with playing cards and puzzles like this:
(He might even contact the school teachers and ask if they notice similar problems.)
I have to come back to my way of teaching reading sheet music:
** READING BY WRITING** and I will mention this in my answers again and again:
You might dictate him a short passage that he doesn't read correct
and tell him to learn it to write and to play by heart too. If he was just lazy then after this period there won't probably
be many similar situations as he will prefer to read it right from the beginning.
Why reading by writing: The pattern of lines and notes will have to pass from his eyes
through in his short term memory into his fingers by writing there
is a greater chance that it will be rest in the long term memory.
- or you give him the task to write down one of his favorite melodies or even an own invention as homework for the next lesson.
One root of analphabetism today is that the pupils are overflood by photo copies in school and don't have time to write down something from the black board.
(I've learnt the most when I started to write my own music with 13 years as wanted to become a "composer".)