Nedda Gilbert, MSW, Educational Consultant, and Author
I am glad you asked this question. This is a frequent concern. It certainly can amp up the anxiety about who's applying where, and who's likely to get in. The short answer is, first, it can impact your chances, and second, it's unlikely they would admit all 30.
But before you panic here are some thoughts. It's possible that some of the attendees to this session were juniors. If so, you can strike them off the list. It's also possible students who went to this session may not apply. Serious students often visit a campus too. You may have seen 30 students in the room - but the question is, who will actually apply? And when in the filing period? This too can impact who wins admission.
It's important you develop a solid list of schools for college. There should be some reaches, mid-reaches and safeties. You don't indicate if you have the right stuff for this fave school. Naviance and a meeting with your guidance counselor will help you not only determine this, but size up the competition and who and how many peers got in last year. This is the best way to get a sense of how many kids they will admit from your high school. And what they are looking for. You need to arm yourself with this data.
As for the number of admits - there is no hard and fast line. At least I don't believe so. However as I said, 30 is unlikely or perhaps more possible at a very large high school with admittance to a state college. Typically, schools need to spread their admits around a large pool of high schools in a geographic area, and also among a diverse range of students. So you are also competing with other high schools in your area - both private and public.
Some colleges will admit a large number of students from one school. As i mentioned, this is more likely to happen in a public high school, and also with large regional powerhouses - like Rutgers University or Penn State. By contrast, if you're enrolled in a private high school the number of admits may be much smaller. A good friend had a daughter enrolled in an elite private school. She was a solid admit for an Ivy. However, she learned that multiples of students had targeted Yale, a school she was also targeting. Because she was not wed to Yale and open to other schools she chose to apply to another Ivy- less popular (that year). She also utilized Early Decision which can offer clear advantages. Her strategy worked and she won early admission.
I would never encourage you to abandon your dreams, however college admission decisions are beyond your control. Stories always circulate about the person who got in and should not have, and the one who should have, but did not. Chasing down the whys of all this would be impossible and not productive. But as I said, getting the statistical data from your school on admits from a particular college the year before should inform your application strategy.
The timing of your application can also help. If the college offers rolling admissions, the sooner you get your application in, the better. This is when there will be plenty of spots still open. Admissions decisions may be more generous at this time. Anther option is to pursue Early Action or Early Decision at this school. This too can advantage you, although Early Decision is binding. You will need to be sure this is your first-choice college.
Finally, I recommend you send a thank you email to the college admissions rep who led your local program. This is the place to mention this is a first choice school (only if it is; mentioning it's your number 2 is sure to get you dinged). If you can't speak to it being your all time fave, you can make mention of majors you are interested in and that you will be sending your application in shortly. This should help you stand out from the crowd. You can take a proactive position in applying to colleges as long as you don't over-do it. One email should suffice unless you have a legitimate reason to contact the admissions rep again (such as submitting mid-semester grades, or sharing news of a recent award).
Hope this helps and provides you a tip or two. Best of luck!