A complete comparison of the national olympiads that matter most for STEM-focused K-12 and high school students with what each one tests, who it's for, and how to pick the right one (or two) for your child.

Why STEM Olympiads Matter

Every year, more students list "AI experience" or "research interests" on college applications. Every year, it gets harder for admissions officers to tell genuine depth from a summer camp certificate. National olympiads solve that problem from the other direction: they're proctored, individually scored, and competitive enough that a real result can't be faked. A USAMO qualification or a USABO National Finalist placement means something specific and verifiable, which is exactly why selective universities weight them heavily.

But "STEM olympiad" isn't one thing. It's at least nine very different competitions testing very different skills, at very different costs and time commitments. This guide breaks down the nine most relevant ones for a STEM-minded student today, so you can figure out which actually fits your child's strengths, not just which one you've heard of.

At a glance

1. USAAIO — USA AI Olympiad

What it tests: Artificial intelligence and machine learning, covering both the underlying math (probability, linear algebra, optimization) and applied programming in Python, NumPy, and PyTorch. Round 1 is a proctored, in-person, three-hour exam blending theory questions with implementation tasks.

Why it's different: USAAIO is the newest name on this list. It launched in 2024 alongside the International Olympiad in Artificial Intelligence (IOAI), but it's already delivering real results. Team USA brought home two gold, three silver, and three bronze medals at the 2026 IOAI in Kazakhstan. As AI becomes one of the most in-demand technical fields, USAAIO is quickly becoming the credential that actually demonstrates depth in it, rather than just familiarity with a chatbot. Recent medalists have gone on to Stanford, MIT, Caltech, and Princeton.

The path: Round 1 (open to all K-12 students, no prerequisite) → Round 2 (qualifiers, held at universities like Harvard and MIT) → USAAIO Camp → Team USA at IOAI, IAIO, and IAI²O.

2027 cycle: Registration is open now through January 31, 2027. Round 1 is February 19, 2027.

Best for: Students who like both math derivation and hands-on coding, and who are drawn to the fastest-growing technical field rather than a more established one. Because it's newer, the applicant pool is currently smaller and less saturated with years of accumulated prep resources than a competition like USAMO or USACO — an advantage for a motivated student starting now.

We provide prep training for USAAIO and the entry AI olympiads around the globe. Details here.

2. USACO — USA Computing Olympiad

What it tests: Algorithmic problem-solving and competitive programming, with data structures, algorithm design, and computational efficiency, submitted in C, C++, Java, or Python and graded by an automated judge.

Format: Four divisions: Bronze, Silver, Gold, Platinum, with three online contests through the season plus a proctored invitational "US Open" championship. Anyone in the world can compete for free with just a usaco.org account; the only restriction is that the training camp and USA team selection (for the International Olympiad in Informatics, IOI) are limited to US pre-college students.

Why it's respected: USACO is one of the most established pre-college CS competitions, and a Gold or Platinum result is a widely recognized signal of genuine algorithmic ability. MIT Admissions, among others, references it directly as a qualifying pathway to the IOI.

The path: Bronze → Silver → Gold → Platinum → US Open (proctored) → Training Camp → Team USA at IOI (4 students) and a parallel team at EGOI (European Girls' Olympiad in Informatics).

Best for: Students who enjoy pure algorithmic problem-solving and want a free, no-barrier-to-entry way to start (anyone can register, no school sponsorship needed at the lower divisions). A natural complement to USAAIO for students interested in both CS fundamentals and applied AI.

3. USABO — USA Biology Olympiad

What it tests: Biology well beyond the AP curriculum, including cell biology, genetics and evolution, animal and plant physiology, ecology, ethology, and biosystematics. Aligned with the International Biology Olympiad's theoretical exam format.

Format: A three-tier progression. The Open Exam is a 50-minute, 50-question multiple-choice exam (roughly 10,000 students participate nationally, administered through a registered school). The top 10% (~600 students) advance to the Semifinal, restricted to US citizens and permanent residents. The top 20 from there attend a two-week residential National Finals training camp, from which a 4-member Team USA is selected for the IBO.

Why it stands out: Team USA has an exceptional track record. Every member of the USA Biolympiad Team has continued to medal at the IBO since CEE began administering USABO, including four golds at the 2026 IBO in Lithuania.

A practical note: Unlike USAAIO, USACO, or NACLO, USABO requires school-based registration with a $125 fee per school, and requires a teacher willing to administer the exam. It is worth checking with your school early, since homeschool students need to arrange testing at a local high school.

Best for: Students with a genuine depth of interest in life sciences who are willing to go well beyond textbook material. Campbell Biology is the standard reference text, and top performers typically study well past it.

4. USNCO — U.S. National Chemistry Olympiad

What it tests: Chemistry well beyond the AP curriculum, covering stoichiometry, thermodynamics, kinetics, equilibrium, oxidation-reduction, atomic structure, bonding, and organic/biochemistry, including hands-on laboratory reasoning, not just written theory.

Format: Run by the American Chemical Society through local ACS sections. The Local Exam (60 multiple-choice questions, 110 minutes, administered by a teacher, typically February–March) determines nominees for the National Exam — a three-part, ~1,000-student event held in April covering multiple choice, written problem-solving, and a laboratory practical. Roughly the top 20 scorers attend a two-week Study Camp, from which a 4-member Team USA is selected for the International Chemistry Olympiad (IChO).

Why it belongs on this list: USNCO is traditionally grouped alongside Biology, Physics, Math, and Computing as one of the long-established "big five" individual national science olympiads, and Team USA's results back that up — all four members won gold at the 2025 IChO in Dubai.

A practical note: Registration runs through a local ACS section and a school-based coordinator, similar to USABO's model. It is worth reaching out to a chemistry teacher early, since each local section can only nominate a limited number of students to the National Exam based on membership size.

Best for: Students with strong AP Chemistry (or equivalent) foundations who enjoy laboratory work as much as theory. The exam's lab practical component makes it distinct from purely written competitions like USAMO or the F=ma/USAPhO written exams.

5. USAPhO — USA Physics Olympiad

What it tests: Physics, starting with algebra-based mechanics and progressing to calculus-based coverage of electricity and magnetism, thermodynamics, fluids, relativity, waves, and nuclear/atomic physics.

Format: Two stages. The F=ma exam (25 multiple-choice questions, 75 minutes, mechanics-focused, roughly 6,000 participants) qualifies the top scorers, historically around 400–500 students — for the USAPhO itself: a much harder, free-response, calculus-based exam split into two 90-minute sections. From there, roughly 20 students are invited to a training camp at the University of Maryland, and five are selected for the U.S. Physics Team at the International Physics Olympiad (IPhO).

Eligibility note: Unlike USACO or NACLO, both exams are restricted to US citizens, permanent residents, or students currently enrolled at a US school, and must be proctored in person at a school (not by a parent or relative, and as of 2026, not by for-profit test-prep centers either).

Best for: Students with strong calculus fluency who want one of the most rigorous, traditionally prestigious physics credentials available at the high school level — this is a demanding, multi-stage filter even to reach the USAPhO stage.

6. USAAAO — USA Astronomy and Astrophysics Olympiad

What it tests: Astronomy and astrophysics across positional astronomy, celestial mechanics, photometry, stellar and galactic astrophysics, and cosmology. It is a physics-adjacent subject with its own distinct syllabus.

Format: Three proctored rounds. A First Round (~75 minutes, ~30 multiple-choice questions, open to anyone, held in February) is followed by the National Astronomy Competition (a ~2.5-hour free-response exam in April, weighted heavily in final ranking) and a Third Round combining theory and practical components after several weeks of online training for top scorers. The top 5 US citizens/permanent residents are selected for Team USA at the International Olympiad on Astronomy and Astrophysics (IOAA).

Why it's worth knowing about: USAAAO is smaller and newer than USAPhO, USAMO, or USNCO, but it's a legitimate, well-organized pathway with a real international team and a strong recent record. The 2025 US team's top scorer won an individual gold medal and was named absolute winner at IOAA in Mumbai. Free weekly online training sessions (led by past IOAA participants and professional astronomers) are a genuine, no-cost resource most families don't know exists.

Best for: Students with a strong physics and math foundation looking for a less crowded pathway than USAPhO — the applicant pool is meaningfully smaller, and the free coaching program lowers the barrier to serious preparation.

7. USAMO / USAJMO — USA Mathematical Olympiad

What it tests: Proof-based mathematical problem solving. This is a different skill from the speed-based multiple-choice of the qualifying exams that precede it.

Format: This is the longest pathway in this competition. Students start with the AMC 10 or AMC 12, and a high score earns an invitation to the AIME (American Invitational Mathematics Examination). Strong AIME performance then earns an invitation to USAJMO (via AMC 10) or USAMO (via AMC 12) — both genuinely proof-based, multi-hour exams. Top performers may then be selected for MOP (Mathematical Olympiad Program), the training ground for the six-member Team USA at the International Mathematical Olympiad (IMO).

What's changing: Starting with the 2026–27 school year, USAMO/USAJMO qualification will be based solely on AIME score, simplifying a qualifying formula that previously combined AIME and AMC scores.

Why it's the gold standard: USAMO is arguably the most universally recognized pre-college math credential in the US, with a selection funnel so competitive that roughly 300,000 AMC participants are eventually narrowed to just six IMO team members.

Best for: Students who love proof-based, non-calculator mathematics and are willing to commit to a multi-year pathway starting as early as middle school (via AMC 8) to be competitive by the time USAMO-level material is reachable.

8. NACLO — North American Computational Linguistics Olympiad

What it tests: Logic and pattern recognition applied to language, decoding the grammar of an unfamiliar language from example sentences alone. No prior knowledge of linguistics, foreign languages, or programming is required; it rewards analytical reasoning more than memorized content.

Format: An Open Round held in person at registered sites across the US and Canada (over 200 sites and 1,700+ students in a recent cycle), followed by an Invitational Round in March for top scorers. The top four to eight US students and top four Canadian students represent their countries at the International Linguistics Olympiad (IOL).

Why it's a hidden gem: Because no background knowledge is required, NACLO is one of the most accessible olympiads on this lis. It is a strong logical thinker with zero linguistics coursework can genuinely compete from a first attempt, which isn't true of USAMO or USAPhO.

Best for: Students who enjoy puzzles and logic more than memorized content, often a great fit for strong readers and pattern-thinkers who haven't necessarily self-identified as "STEM kids" yet. Also a low-commitment way to explore computational thinking before committing to something like USACO or USAAIO.

9. USESO — US Earth Science Olympiad

What it tests: Earth and environmental science across geology, meteorology, oceanography, and astronomy, an interdisciplinary mix that doesn't map neatly onto a single AP course.

Format: A spring National Open Exam (pay-what-you-can registration, $25 standard or $5 for financial need) determines invitations to a week-long residential Training Camp (top 40 scorers, held in Tulsa, Oklahoma in recent cycles). From camp, USESO selects a 4-member main team plus up to 4 guest team members for the International Earth Science Olympiad (IESO).

A practical note: Training Camp costs $2,600 (need-based financial aid is available), making it a bigger financial commitment than most others on this list if a student advances that far — worth planning for if your child is seriously pursuing this path.

Why it's underrated: Team USA has a genuinely strong IESO track record, including first-place finishes and multiple gold medals in past cycles, despite Earth science getting less attention than physics, math, or biology in typical STEM-track conversations.

Best for: Students interested in environmental science, geology, or climate-related fields who want an olympiad that rewards interdisciplinary thinking over deep specialization in one subject.

A note on climate-specific competitions: Families researching Earth science options sometimes come across the ClimateScience Olympiad, a global (not US-specific) competition that ran annual cycles from 2021 through 2024, with an award ceremony at COP26 and a sponsored trip to COP29 for 2024 winners. As of this writing, no 2025 or 2026 cycle appears to have been announced, and the program looks to be on pause — worth confirming directly with the organizer before counting on it as an active option.

How to Choose

A few rules of thumb, rather than a one-size-fits-all answer:

• Match the skill, not the subject label. USAMO, USAPhO, and USAAAO reward calculus-heavy, proof- or derivation-based thinking. NACLO and the early stages of USACO/USAAIO reward logical pattern recognition and can be approached with less formal background. USABO, USNCO, and USESO reward broad factual depth and willingness to read well beyond a textbook — with USNCO adding a hands-on laboratory component the others don't have.

• Consider the barrier to entry. USAAIO, USACO, USAAAO, and NACLO have no school-registration requirement or fee to start. A highly motivated student can register directly. USABO and USNCO both require a school sponsor and a fee; USAPhO and USAMO run through school-administered exam infrastructure.

• Newer isn't worse, and smaller pools can be an advantage. USAAIO is the newest name here, but it already has a strong Team USA medal record and sits in a field — AI — with rapidly growing relevance to both academia and industry. USAAAO, similarly, has a meaningfully smaller applicant pool than USAPhO or USAMO while offering a comparably real international pathway (plus free coaching most families don't know about). For a student choosing where to specialize now, both trajectory and competition density are worth weighing alongside an olympiad's age or prestige.

• It's fine to try more than one. Many strong candidates for USACO also do well at USAAIO, since both reward programming fluency; strong AMC/AIME performers often have an easier time with USAPhO's or USAAAO's calculus-based sections; USABO and USNCO overlap for students strong in both biology and chemistry. Overlap is common, and a broad first year (say, trying NACLO or an olympiad's easiest tier) is a reasonable way to find out where a student's strengths actually are before committing deeply to one.

Getting Started with USAAIO

Of the seven, USAAIO is the one we work with directly. If your child is drawn to AI and machine learning specifically, AIClub's Research Institute pairs students with PhD mentors for custom 1:1 USAAIO preparation, built around your child's actual starting point, not a generic curriculum. Registration for the 2027 competition closes January 31, 2027.

Interested in the AI Olympiad? Contact us for a free consultation.