I've been in the college-bound space for decades, first as a parent going through the process twice and then as co-founder of College Confidential, the busiest website in that space (40 million pageviews last month). That business was sold to a large international firm in 2008, though I consult for the firm and remain engaged with the community.
That business was one product of my entrepreneurial focus on direct marketing and digital marketing.
Before answering your question directly, I'd offer a bit of experience-based advice. I've seen many apparently great business ideas in the college space fail because of a surprising unwillingness of most students/parents to pay for helpful tools.
I'm at a loss as to why families confronting one of their most important decisions and an expense that will run into the tens or hundreds of thousands of dollars would balk at spending modest amounts of money to get a better outcome.
To be certain, students who are candidates for ultra-selective schools and whose families have substantial resources will pay for things like test prep and occasionally advising services, but this group is quite small compared to the entire population of college-bound students.
I could list a series of companies that offered a paid product for this market and either failed or succeeded only after converting to a free model monetized in some other way.
Another megatrend to be wary of is the likely disruption of traditional higher ed by a variety of forces: unsustainable tuition levels, questionable ROI for a 4-year diploma in many fields, the rise of credible online higher ed options, probable closure of many colleges, etc. If your product can ride these waves, so much the better. If it's focused on the traditional system and process, watch out.
Enough doom and gloom... let's talk about your product and how to market it.
Assuming that the product and price point will indeed create revenue if it can get in front of families, I'll throw out a few ways you could proceed.
I assume that you don't want to do this as a solopreneur, creating your brand, website, outreach plan, etc. The skills involved are the full range of digital marketing activities, and even coordinating the work of others (website creation, search engine optimization, paid ads, content marketing, influencer outreach, etc.) takes both time and expertise.
One approach would be to find a co-founder that has both the time and skill that would bring the plan to fruition. This is a bit of a unicorn hunt, but there are websites and local meetups (in cities with entrepreneurial cultures) that bring co-founders together. The revenue potential would have to be high enough for a talented person to commit to it. They would need to see a short path to revenue (so they can be paid) as well as an exit strategy.
Another would be to find a company successfully selling in the space and work a deal to market your product. For the reasons I mentioned above, this may be difficult.
A third variation would be to partner with a company that has relationships with high schools, guidance counselors, etc. I'd expect they wouldn't be interested in marketing an inexpensive add-on as a standalone item. But, they might consider some kind of outright purchase or royalty deal if bundling it into their offering added value for their customers.
An approach that might work for this situation is crowdfunding, e.g., Kickstarter or Indiegogo. You could offer the product, test the waters, and let customers fund its production. If the interest is too low to be viable, you'll have spent some money (to create a credible campaign) but the damage will be limited. This could be combined with a "find a co-founder" approach if you aren't comfortable creating the campaign yourself. Designing a successful crowdfunding effort is as demanding as launching a business. Today, building demand with social media, establishing relationships with influencers, creating a great video, etc. are table stakes, not frills.
It's hard to be more specific without knowing more about the product. Physical products are different from digital products. One-time purchases are different from subscription models. A product that appeals to Ivy aspirants is quite different than one designed for students focused on in-state public institutions.
Good luck with your product! I can assure you, knowing you are helping families through the confusing and difficult college process is a reward in and of itself.
I'd be happy to talk with you if you want to explore any of these ideas in more detail.