Why the White House Picked 4th Graders For Free National Park Admission

— -- President Obama announced a new initiative today to encourage young children to visit national parks -- but it’s not all young kids.

It's specific to 4th graders.

The program, 'Every Kid in a Park initiative,' allows for free admission for fourth graders and their families to all national parks for a full year.

But what is so special about those awesome 9 and 10 year olds?

According to a White House official, the school grade was decided on for “logistical, educational and instructional reasons.”

“NPS and other land and water agencies already have 4th grade programming in place in many locations,” the official said. “Many states focus on state history during the 4th grade, which aligns well with what NPS and other land managers have to offer.”

The White House also points to 4th graders only having one teacher at that age, making it easier for them to reach the group and research which shows the earlier a youth connects with the outdoors the better for their development long term.

The official pointed to age 11 as the last chance to make those important impacts and building of a relationship with nature.

Teenagers younger than 16 can already access the parks for free, but there is a fee for adults accompanying them and for the family car. An annual nationwide family vehicle pass is $80.

The announcement comes as Obama is set to designate three new National Monuments today.

ABC News' Devin Dwyer contributed to this report.