TL;DR
This blog compares RSI, SSP, and COSMOS to help you choose a summer science program that fits your goals, budget, and eligibility. RSI is a highly selective, free program; SSP offers team research and need-based financial aid for U.S. and international students; and COSMOS is a shorter, lower-cost option for California students. You can use the comparison table and application tips to decide where to apply and what to do if you don’t get in. If you’d like online research mentorship during the school year, you can apply to Horizon to work on a research project with a PhD mentor.
RSI vs. SSP vs. COSMOS – which one’s the best?
If you’re comparing RSI, SSP, and COSMOS, you should look at the cost, eligibility rules, research format, and application process. RSI offers free individual research at MIT and a new Stanford site in 2027, SSP focuses on team research, and COSMOS gives California students a shorter, cluster-based STEM experience. You can use the table below to see which program fits your goals:
| Feature | RSI | SSP | COSMOS |
| Who runs it | Center for Excellence in Education (CEE) | SSP International, a nonprofit founded in 1959 | University of California |
| Subjects | Math, science, engineering, and STEM research | Astrophysics, Biochemistry, Bacterial Genomics, and Cell Biology | STEM topics across different research clusters |
| Location and format | MIT, as well as Stanford University for 2027; individual research | Residential, team-based research at college campuses in the U.S. and Canada | Residential at UC Davis, UC Merced, UC San Diego, UC Irvine, UCLA, or UC Santa Cruz |
| Length | 6 weeks | 5 weeks | 4 weeks |
| Dates | June 20 to July 31 at MIT; June 27 to August 7 at Stanford | 2027 dates not announced. The 2026 sessions ran from June 8 to August 1 | 2027 dates not announced. The 2026 session ran from July 5 to 31 or August 1, depending on the campus |
| Cost | Free | $11,800 for 2026. The 2027 fee hasn’t been announced. A $3,000 stipend is available to a limited number of students | $5,793 for 2027 |
| Financial aid | No tuition charged | Covers 100% of demonstrated need for admitted students | Partial or full need-based aid is available |
| Grade and age eligibility | High school juniors aged 16 or older | High school juniors aged 15–18 during the program | Rising 9th–12th graders |
| Citizenship and international students | U.S. citizens and permanent residents apply directly. International applicants use their country’s selection process | International applicants are welcome | Only California residents attending California high schools can apply |
| Selectivity | <2.5% acceptance rate; CEE reports more than 3,000 applicants each year. The MIT cohort has about 100 students, with 50 additional places planned at Stanford for 2027 | No official acceptance rate published. SSP admitted 720 students across 20 programs and 13 campuses in 2026 | About 16%, according to a March 2026 UC report to the California Legislature |
| Application deadline | December 11, 2026, at 11:59 p.m. | January 2027 for international applicants and February 2027 for domestic applicants. Exact dates to be announced | January 6 to February 5, 2027 |
| What you produce | A written research paper and a conference-style oral presentation | Team research findings presented at the end | A cluster research project and Certificate of Completion. No grades or academic credit |
| Best for | Students who want free, intensive individual research and meet the eligibility rules | Students who want team-based science research and need financial aid | California students seeking a shorter, lower-cost residential STEM program |
Sources: CEE’s RSI 2027 announcement, SSP application details, SSP fees and financial aid, COSMOS dates and deadlines, and COSMOS 2026 fees. Checked October 2026.
Each program will work well for different goals and circumstances. RSI is tuition-free and highly selective, SSP offers team research with substantial need-based aid, and COSMOS is a shorter option only for eligible California students. You can compare the eligibility rules and research format before deciding where to apply.
How are RSI, SSP, and COSMOS different?
How the research works: Each program offers a different way to explore science. At RSI, you’ll work with a research mentor on an individual project. At SSP, you’ll join a team of three and work on a shared research problem, analyzing data and presenting your findings with your teammates. At COSMOS, you’ll join a topic cluster, a group focused on a specific STEM subject, and participate in lectures, lab work, and a group research project.
Who can apply: Your grade and location can help you narrow down your options. RSI and SSP are for high school juniors, and COSMOS accepts students in grades 8–12 who live in California and attend a California high school. You must check the course prerequisites before applying, as some SSP tracks and COSMOS clusters require you to have completed specific classes. If you’re a sophomore, you can prepare to apply to RSI or SSP next year. You can also apply to COSMOS sooner if you meet its requirements.
Cost: The cost is different for all 3 programs. RSI is free, SSP offers need-based aid that can cover the full fee, and COSMOS charges tuition but offers partial or full aid only to eligible California students. Need-based aid means that the amount you pay depends on your family’s financial situation. Qualifying SSP students can attend for free, and COSMOS aid can lower your tuition. You should check the latest fees and aid rules before applying, as costs can change each year.
Which is better for biology?
Your best option depends on the type of research you want to do. SSP offers biology-focused tracks in Bacterial Genomics, Biochemistry, and Cell Biology. COSMOS has life science clusters at some campuses, while your RSI research topic depends on your mentor and project. Think about whether you’d prefer a set biology track, a campus-specific cluster, or an individual project guided by a research mentor.
Cost and financial aid compared
| Program | Program fee | Application fee | Who gets aid | Travel help |
| RSI | Free | $75 (non-refundable) | No tuition to cover | Check with CEE for travel support details |
| SSP | $11,800 for 2026; 2027 fees expected in December 2026 | Free | Need-based aid can cover the full fee. Families earning $75,000 or less qualify for free attendance, while those earning under about $140,000 may qualify for a discount | Travel aid is available. A limited number of $3,000 lost-wages stipends help students who usually work during the summer. No loans are offered |
| COSMOS | $5,793 for 2027 | $48 (fee waivers are available) | Partial or full need-based aid for eligible California residents | Check the current financial aid terms for travel support details |
Sources: CEE, SSP fees and financial aid, and COSMOS program fees. Checked October 2026.
Need-based aid means your family’s income and financial situation help determine how much you’ll pay. RSI is free, SSP can cover the full fee for eligible students, and COSMOS costs less than SSP before financial aid. You should also keep in mind that COSMOS is only open to eligible California residents. Each program has different eligibility rules, so you need to check the latest requirements before applying.
If you’re looking for more programs with no tuition, you can explore 16 Fully-Funded STEM Programs.
Which one fits you?
Your best option depends on your grade, location, research interests, and budget. You can start by checking which programs you’re eligible for, then compare their research formats and costs.
| If you… | Consider |
| Are a high school junior with strong math skills and want to work on an individual research project with a mentor | RSI |
| Want to work in a small team on a shared research problem in astronomy, genomics, biochemistry, or cell biology | SSP |
| Live outside the U.S. and want to join a summer science program | SSP, which accepts international applicants, or RSI through your country’s selection process |
| Live in California and are in 9th or 10th grade | COSMOS, if you meet the campus and cluster requirements |
| Need a free or affordable program | RSI, SSP with need-based aid, or COSMOS with financial aid if you’re eligible |
| Are a high school senior | RSI and SSP aren’t options because they’re for juniors. If you’re in California, check the latest COSMOS eligibility rules. Otherwise, you can consider year-round research programs |
| Want to continue research online during the school year | Horizon, which pairs you with a research mentor for a project you can work on outside the summer |
You can apply to more than one program in the same year if you meet each program’s eligibility requirements and have time to complete the applications. COSMOS is limited to eligible California students, while RSI and SSP have their own grade, citizenship, and application rules.
You should plan ahead because each program has different essays, recommendation requirements, prerequisites, and deadlines. Start with the earliest deadline and leave enough time to prepare each application.
If you’d like to work on a research project with an online mentor during the school year, apply to Horizon. You can also explore 15 Prestigious STEM Programs for more options.
How do I apply to RSI, SSP and COSMOS? Do they have the same application?
RSI, SSP, and COSMOS look for different things in the applications, so you need to prepare for each one separately. RSI focuses on your academic record, test scores, and recommendations. SSP looks at how well you’ve prepared for your chosen research track, and COSMOS asks about your interests and readiness for its coursework.
| Application component | RSI | SSP | COSMOS |
| Essays | Written responses in the application | Application responses about your interest and preparation for your chosen track | Personal statement and responses about your cluster choice |
| Recommendations | Three from math or science teachers or a research supervisor. If you’ve completed a research project lasting four weeks or more, one recommendation should come from that supervisor | One recommendation from a math or science teacher at your school is required. A second is strongly recommended | One math or science teacher recommendation is required. Two are recommended |
| Transcript | Official transcript | Official transcript | Upload an unofficial transcript with your application. If accepted, submit an official transcript showing your unweighted GPA. If you’re entering 9th grade, you’ll also need your 7th-grade report card |
| Test scores | All standardized test scores, including PSAT, SAT, ACT, and AP | No standardized test scores for 2027, except English proficiency scores for international applicants | No standardized test scores are required |
| Other | Strong math and science preparation. CEE recommends PSAT Math 740+, SAT Math 750+ and Evidence-Based Reading and Writing 700+, or ACT Math 33+ and verbal 34 | Choose one research track and meet its coursework prerequisites | Parent or guardian consent is required. COSMOS says a typical applicant has a GPA of 3.5 or higher |
| Deadline | December 11, 2026, at 11:59 p.m. | January 2027 for international applicants and February 2027 for domestic applicants, as currently anticipated | February 5, 2027, at 11:59 p.m. |
| Decisions | All applicants are notified in March | Usually mid-March for international applicants and mid-April for domestic applicants | March 25, 2027, at 5 p.m. |
Sources: SSP application details, SSP coursework and test requirements, COSMOS application requirements, and COSMOS dates and deadlines. Checked October 2026.
A timeline for applying to all three
If you’re a junior planning to apply to RSI, SSP, and COSMOS for summer 2027, you can use this timeline to organize your applications:
- Fall 2026: Ask teachers for recommendations 4-6 weeks before each deadline. Contact your RSI recommenders before Thanksgiving so they have enough time.
- Early December 2026: Submit your RSI application by December 11. Check that your transcript, test scores, essays, and recommendations are complete.
- December 2026 – February 2027: SSP applications open in December, and the expected deadlines are in January (for international applicants) and February (for domestic applicants). COSMOS applications open on January 6 and close on February 5.
- March – April 2027: Check your admission decisions. SSP decisions are usually expected in March (for international applicants) and April (for domestic applicants). RSI decisions are released in March, and COSMOS will announce its results on March 25.
You should ask for recommendations early instead of waiting until the deadline. Teachers might be writing recommendations for several students, and each application has different requirements.
For tips on essays, recommendations, and showing why you’re a good fit, you can read How to Get Into a Top High School Research Program: 10 Tips.
Is RSI harder to get into than SSP or COSMOS?
RSI is the hardest of the three to get into, with an acceptance rate below 2.5%. It’s free, has a small cohort, takes only high school juniors, and draws applicants from the U.S. and other countries. Here’s how the three programs compare:
| Program | Acceptance rate | Applicants and cohort size |
| RSI | Under 2.5% | More than 2,500 U.S. and 600 international applicants each year. About 100 students at MIT, plus 50 more at Stanford for 2027 |
| SSP | Not published | Around 700 students admitted across 13 host campuses in 2026 |
| COSMOS | About 16% | Six UC campuses, open only to California residents at California high schools |
Sources: CEE RSI application FAQs, SSP application details, SSP host campuses, and UC report to the California Legislature on COSMOS. Checked October 2026.
To get into RSI, you’ll need strong grades, solid math and science skills, and recommendations that show you’re ready for advanced research.
SSP is also selective. It looks for students who are prepared for their chosen research track and can work well in a team. Since SSP doesn’t publish an acceptance rate, treat any percentage you find online as an estimate. COSMOS is competitive too, but only California residents at California high schools can apply, and you’ll need to pick a research cluster at one of its six UC campuses.
Acceptance rates alone don’t give you the full picture, since each program has its own eligibility rules, cohort size, and application requirements. All 3 programs are prestigious, but the most selective one isn’t automatically the best fit for you. What you learn, the research you complete, and how you explain your work matter more than the program’s name.
For more options, you can read Most Prestigious Summer Research Programs With Low Acceptance Rates. If RSI is your main goal, check out Everything You Need to Know About RSI for details on eligibility, applications, and preparation.
What to do if you don’t get in – RSI, SSP, and COSMOS alternatives
Not getting into RSI, SSP, or COSMOS can be disappointing, particularly after spending weeks working on essays and recommendations. All 3 programs reject many applicants, including students with strong grades, test scores, and research experience. Rejection from one program doesn’t mean you’re not capable of doing research or pursuing science.
Here are five ways to move forward:
1. Start a research project during the school year
You can work with a research mentor outside the summer program cycle. Horizon’s 1:1 PhD Labs offer online, one-on-one guidance from a PhD scholar or professor over several months. You’ll work toward a research paper of around 20 pages. Unlike residential summer programs, this option will allow you to work online with a mentor for a longer period. You can learn more in Can You Do Real Research Online in High School?.
2. Apply to other selective programs
You should look for research programs with later deadlines that are still accepting applications. Start with The Most Competitive Research Programs and The Most Competitive Summer Programs. Check each program’s current deadlines and eligibility rules before applying.
3. Look for free university programs
You don’t have to spend thousands of dollars to gain research experience. You can check out 14 Free University Science Summer Programs, as well as guides to the Simons Summer Research Program, Clark Scholars, and Stanford SIMR. Compare their costs, eligibility rules, and deadlines before choosing where to apply.
4. Enter a research competition
If you’ve completed a research project, you can share your findings through a competition. Explore 15 Research Competitions for High School Students and check which ones accept your subject, project type, and grade level.
5. Improve your next application
Review your essays, coursework, and research interests to find out where you can improve before the next application cycle. You should focus on building useful skills and completing research you’re interested in, instead of collecting program names for your résumé. If you’re still eligible, you can apply again with a clearer idea of the research that you want to pursue.
Frequently asked questions
On paper, yes. RSI accepts fewer than 2.5% of its applicants, according to CEE. MIT admitted 4.6% of applicants for the Class of 2030, which was 1,299 out of 28,349, according to The Tech. RSI is a 6-week summer research program for high school juniors, and MIT is a university with a different application process, goals, and student population. You should make sure that RSI matches your research interests and focus on preparation instead of comparing it to college admissions.
Yes, you can apply to all three if you meet their eligibility rules. RSI and SSP are for high school juniors, while COSMOS is limited to California residents attending California high schools. SSP also requires you to choose one research track, so check its course prerequisites before applying.
Yes, SSP is a respected nonprofit program founded in 1959, with a long history of team-based science research. What matters most is what you learn, the research you complete, and how you explain your experience, not just the program’s name.
International students can apply to RSI and SSP, but the requirements differ. RSI applicants must apply through their country’s selection process. SSP accepts international students, who have an earlier deadline and may need to submit English proficiency scores. COSMOS is limited to eligible California residents attending California high schools.
For summer 2027, COSMOS tuition is $5,793, along with a $48 application fee. Eligible California residents can apply for need-based financial aid, and application fee waivers might be available. You can check the official COSMOS fees page for costs and financial aid rules for your application year.
These programs can show that you’re prepared for STEM research, but getting accepted doesn’t guarantee an advantage in college admissions. What you learned, the research you completed, and how you explain your work matter more than the program name. You can read Do Summer Research Programs Actually Help with College Admissions? for more information.
RSI and SSP only accept high school juniors, so you can’t apply if you’re already in your final year. For summer 2027, COSMOS accepts rising 9th–12th graders. You need to be entering 12th grade in fall 2027, not graduating in spring 2027. You can still work on a research project during the school year with a mentor. Horizon accepts students in grades 9–12 and offers online, one-on-one mentorship with a PhD scholar or professor over several months. Apply to Horizon to explore this year-round option.
Picking your program
You can choose RSI for a free, highly selective research experience, SSP for team research with strong financial aid, or COSMOS for a shorter summer program if you’re an eligible California student. Compare each program’s research format and eligibility requirements to find which one works best for you.
If you don’t get into these programs, you can still work on a research project online with a PhD scholar or professor through Horizon. Apply to Horizon or join an info session to learn more.
Resources
Official program sources
- Research Science Institute (RSI) application page, Center for Excellence in Education
- SSP fees and financial aid
- SSP frequently asked questions
- SSP host campuses
- California State Summer School for Mathematics and Science (COSMOS), UC statewide site
- UC Irvine COSMOS FAQs
- UC report to the Legislature on COSMOS
More from Horizon
- The Most Competitive Research Programs
- The Most Competitive Summer Programs
- 16 Fully-Funded STEM Programs
- 14 Free University Science Summer Programs
- 15 Research Competitions for High School Students
- 15 Prestigious STEM Programs
- 35 Summer Research Programs
Image source: Research Science Institute