That website you refer to (greatschools.org) gives my kids' HS a 6 out of 10. But rankings like the Washington Post's Challenge Index regularly score it as one of the top high schools in the country. (And I tend to agree with WaPo, it is a truly excellent school.) So take those internet ratings with a grain of salt. Far better to get off your computer and talk to actual parents.
This. My HS is rated a 5 on that website. I can tell you from personal experience that that is full of shit -- I went there, I was a NMS and went to a nationally-ranked SLAC, my DD goes there now, she is on the honors track and in challenging AP classes, etc. etc. etc. As a junior, for example, she will have Project Lead the Way (two engineering classes), AP Physics, and Calculus AB, along with AP English and AP History. And she has a great friend group of interesting, quirky kids.
The problem is, as many others have said, that we just draw from more of a mixed area than the higher-ranked schools -- we have more poor kids and minorities who have not had the same advantages growing up and so who don't perform as well on those stupid state standardized tests. You have the same issue -- looks like you are more toward the Elkridge side than the Columbia side, and there is a pretty good socioeconomic split depending on which side of I-95 you are on (yes, I am nearby -- I don't know that particular school, though, but I am hypothesizing based on the similar demographic split to my area). But if you have a smart kid who is on the honors track, that will not affect you at all.
I would say, before you freak out, go visit the school talk to the principal, talk to parents who have actually sent their kids there. In our neighborhood, we have a MS that everyone talks trash about, primarily because it draws from poorer areas -- well, lucky us, my son is zoned to go there next year. (Irony alert: this highly-disparaged MS scores a point *higher* on this website than the HS that these same people happily send their kids to). But if you actually talk to the teachers, they *love* the school, and the parents who didn't run away speak well of it as well. Yeah, I'm not particularly happy, but it's because of the distance (he can't walk home safely -- no sidewalks, would have to cross a major highway) and the social aspects (they divided our neighborhood so that literally all of his friends are going to the other MS). Academically, he will do fine.