11th-12th Grade (17-18)

Physical Development : Changes in the body

By the time students are in 11th and 12th grade, they have grown and developed quite a bit.
Most girls are typically as tall as they are going to get by these grades. They are still adding a natural amount of fat in areas like the hips, arms, breasts, and legs.
The boys are usually still growing, but slowing down, and gaining muscle.
For the most part, they have their adult bodies by these grades, but they are not quite ready for adulthood.
By this time, students, in general, have reached sexual maturity.
11th and 12th graders are more agile and less clumsy than students in other grades.
They have developed visual-spacial coordination.

Social Development: Way an individual relates to others

At 11th grade and especially by 12th grade, students value committed relationships.
Friendships and romantic relationships are taken more seriously.
They are starting to look at moving on from "teen" activities.
They are developing community consciousness.
They look for guidance only from adults by this time.
Peer pressure is becoming less of an issue.
Arguing is a popular thing to do in these grades.

Cognitive Development: Changes in thinking, reasoning, and decision making

They start making decisions on their own at these grade levels.
Long-term goals and future plans are being to be made.
They start making their own schedules.
Abstract thinking is becoming a regular event.
Their logic and reasoning skills expand during these grades.
They can explain their reasoning for doing something.
Juniors and Seniors in high school have definite study methods.
Hypothetical and Deductive thinking skills have been established.

Personal Development: Changes in personality

Activities that they have done in the past are starting to loose appeal.
Looking back at achievements brings them enjoyment.
They look for recognition when it comes to bigger situations.
They expect to be treated as fully grown.
Students in these grades tend to sleep more than they have in the past.
They are getting more comfortable with being their own person.

Sources

"Normal Development: Late Adolescence (18-20 Years old)." Wayne State University Group, http://www.wsupgdocs.org/family-medicine/WayneStateContentPage.aspx?nd=1602

Stewart, Janelle. "18- to 19-year-Olds: Ages and Stages of Youth Development." Michigan State University, http://www.canr.msu.edu/news/18_to_19_year_olds_ages_and_stages_of_youth_development.

"Wellness by Age: 17-18 Years." children's health, https://www.childrens.com/health-wellness/wellness-by-age-seventeen-to-eighteen.