I hope this is the right place to ask this question.

My brother (15M) is having a hard time in school. He's making As, and he is in gifted, but he struggles on reading tests. For instance, he sat down with my mom and read a chapter of a book for school. My mom then asked him to summarize it, which he did accurately. The next day, they had an open book test over that chapter, and he got a 1/4. Another chapter test he got a 2/6. My mom asked him and his teacher what went wrong, and he said he just ran out of time, and he only got to the questions he answered correctly. He's had some difficulties paying attention to and relaying instructions being given in the past but has been doing doing better this year. When he was in pre-school he has a speech impediment and worked with a speech therapist for a time to fix that. Also, he was diagnosed with Auditory Processing Disorder, and when he took tests in elementary school he was allowed to do so in a separate location. Recently, my mom had to do some sort of Dyslexia training for teachers, and she now thinks he might have that. Additionally, our bio dad has ADD. Any ideas?

Additional info:

Height: 5'10"

Weight: 125 lbs

Race: White/Hispanic