Hello,
Thanks for the D2D. Yes. It is likely that he might have Obstructive Sleep Apnea. He seems like he has stoppages in breathing at night and he might have nose congestion which explains his mouth opening during sleep.
Because of the stoppages in breathing at night, his brain does not get enough oxygen at night, hence this affects his daytime concentration, he has a short attention span and poorer memory with poorer academic performance.
In children, because of the sympathetic overdrive, they are hyperactive during the day and cannot focus on any task.
Might be prudent to consult a Sleep Specialist as soon as possible.