So, what does it take to get admitted? GPA? Scores? APs? ECs?
Have a son who is a jr in HS and interested. He’ll have around a 4.3-4.5. He’ll have at least 11 APs, several honors classes, varsity baseball, club baseball, started an annual 3v3 charity basketball tournament, DECA state competitor, works at baseball club at front desk and asst coaching…
Here’s the link to NU’s common data set: https://enrollment.northwestern.edu/pdf/common-data/2017-18.pdf
Starting on page 8 you can see average test scores along with what the university feels is most important.
NU’s acceptance rate fell to 8.4% last cycle so should be considered a reach for any student.
https://dailynorthwestern.com/2018/03/24/campus/northwestern-acceptance-rate-falls-to-8-4-percent/
@Grandmom1 - Per @momofsenior1 's article linked to above, if your son applies ED, the odds go up to @ 26.5% admissions rate. That’s like hitting at a .265 clip as opposed to a last off the bench .064!
My youngest played baseball for a top team in the state, was admitted ED, & thanks to all his AP scores, graduated with a MS in 4 years. He likes to tell people that his weakest link for admission was a slider, low and away late in the count… 
But as @momofsenior1 writes, any app to a top school should be considered a stretch, so have some safety schools ready to play.
Good Luck to your son. Tell him to step up to the plate and take a swing at it.
Make sure you run the Net Price Calculator to see if NU is affordable.