Why are boys most likely to have adhd than girls?

Unknown: Inattentive subtype without hyperactivity, however, is much more prevalent in girls.

Teacher referrals: Boys are labeled hyperactive because until about the age of 8 their brain is developing skills that require movement. Girls during those years are developing social skills. Teachers are largely female and few know how to motivate males and expect them to sit and listen. On top of this the school district is paid more when their students are labeled adhd. As a result teachers refer more boys.

The ratio of boys:: Girls with adhd, historically 3:1, is probably skewed because the presentation differs. Boys are more likely to have adhd-primarily combined type, with 6/9 or > significant symptoms of both inattention & hyperactivity/impulsivity. Girls are more likely to have adhd-primarily inattentive type. Studies show that up to 75% of cases in girls may be missed. See chadd.Org for details on diagnosis.