My job requires me to visit high schools all over the united states. In fact, my first high school visit will be on Sept. 10th this year.
There is some truth to what u see and some not truth.
Lockers, yes. Schools in wamer climates look way different than schools in colder climtaes. For example, a high school in southern Cal or Florida is usually more open and lockers can be outside, where as in northern climes such as NY, Philly, Chicago, etc....the schools are all enclosed. Usually big campuses, sometimes with several buildings.
Extra-carriculars are par for the course. That's part of the high school experience. A lot of colleges and universities like to see students who were involved in high school, whether it be community service, athletics, clubs, organizations supporting a cause, etc... different clubs for all kinds of interest, whether is be cheerleading, football, mathletes, drama club, LGBT awareness club, school newspaper, school yearbook, pep squad, band, stage crew, video game club, etc. At one high schooll I was at there was a club for people who enjoyed speaking with British accents..they would gather and just speak in a british accent to eachother, that's it lol. . The idea is to keep the student engaged in something productive versus going home and sitting in front of the TV or computer. Also, to connect with students with similar interests.
A typical, well-off suburban american high school will offer tons of extra-curriculars for their students. Low-income money-strapped schools do not offer as many opportunities, unfortunately.
It all depends also on whether the school is private or public, religiously-affiliated or not and a host of other things. High schools here in Cal tend to be shit. Not all of them though, but a sizeable majority. Same goes with Florida. Where I hear high schools in Massachusetts and New York are apparently really good.
But, it's not all like "the hot foot ball star dating the slut cheerleader, etc.." type of thing u see on TV