TL;DR
The American Computer Science League is an online computer science competition with four regular-season contests across five divisions. You can compete through your school, club, or organization, with the format depending on your division and ranging from computer science questions to programming problems. The top-performing students can qualify for the ACSL Finals, and the separate Summer Coding Challenge gives you three programming problems to solve within four hours. If you want to build a sustained independent computer science project with 1:1 mentorship, explore the Horizon Academic Research Program. If you want to build a sustained independent computer science project with a mentor, explore the Horizon Academic Research Program.
Competitions are one of the most practical ways to build your skills, see where you stand when you’re tested, and strengthen your college application. If computer science interests you, the American Computer Science League (ACSL) should be on your radar. It has been running computer science and programming contests for K–12 students for decades, with participants from schools and organizations around the world. You’ll solve problems across topics like number systems, Boolean algebra, data structures, graph theory, and programming. For more options, check out 15 programming competitions for high school students.
How does ACSL work, from registration to the Finals?
The regular ACSL season consists of four online contests held across the academic year. Your school, club, or organization registers teams through an advisor. The advisor can be a teacher, parent, or another adult with computer science experience. Students do not register their own regular-season teams.
ACSL currently has five regular-season divisions:
- Senior: designed for high school students with programming experience
- Intermediate: designed for high school students with little or no programming experience and advanced junior high students
- Junior: designed for junior high and middle school students, with no student beyond grade 9 eligible
- Classroom: open to students in all grades and designed for classes without a major programming component
- Elementary: open to students in grades 3 through 6
Within each division, an advisor can register a 3-score or 5-score team. A 3-score team can have up to six students, while a 5-score team can have up to ten. The team score for each contest is calculated from the best three or five student scores, depending on the team’s format. A student can participate on only one team and in only one division per season.
The four contests are available online through HackerRank during set windows. For the Junior, Intermediate, and Senior divisions, each contest has a short answer section and a programming problem. The short answer portion is generally 30 minutes, while the programming problem has a 72-hour running time. Classroom has a 50-minute short answer test, and Elementary has a 30-minute non-programming test.
For the current season, the four contest windows run from October through May, followed by an online invitational Finals on May 29. ACSL says that top-scoring students across the divisions are invited to the Finals.
The Finals are individual, even though regular-season students compete through teams. ACSL’s current FAQ says students who qualify receive a separate Finals invitation, and Finals participants compete for prizes and certificates.
Regular Season vs. Summer Coding Challenge
| Format | Divisions | Structure and length | What’s evaluated |
| Regular Season | Senior, Intermediate, Junior, Classroom, Elementary | Four contests across the academic year. Junior, Intermediate, and Senior include short answer questions plus a programming problem. Classroom and Elementary use non-programming questions. | Computer science concepts, reasoning, and programming in divisions that include a coding problem |
| Summer Coding Challenge | Rookie and Veteran | Three programming problems completed in one four-hour window | Programming ability, problem solving, and the correctness of submitted solutions |
The Summer Coding Challenge is separate from the regular ACSL season. It is open to students who have not yet entered college and has two divisions. Rookie is for students with no more than one year of coding experience, while Veteran is for students with more experience.
What’s different about the Summer Coding Challenge?
The Summer Coding Challenge is much more focused on programming than the regular ACSL season.
You solve programming problems during a designated online competition window. You can choose when to begin during the official competition period, but once you start, you have four hours to complete the challenge. You need a computer with a webcam, a reliable internet connection, and either Google Chrome or Microsoft Edge.
The current Summer Coding Challenge costs $20 for either division. All participants receive a certificate of participation, and the top three finishers in each division receive prizes.
The challenge uses HackerRank Secure Mode. ACSL currently lists several integrity controls, including full-screen enforcement, tab switch alerts, copy and paste restrictions, multiple-monitor checks, and webcam image analysis. These controls are part of the competition’s effort to ensure that submissions represent the participant’s own work.
The Summer Coding Challenge therefore makes more sense if you specifically want a concentrated programming contest. The regular season gives you a broader computer science experience across several topics and spreads the contests across the school year.
How competitive is ACSL, and what counts as “acceptance” here?
ACSL does not have a conventional acceptance rate for its regular season.
The regular season is open for registration through schools, organizations, and teams that meet ACSL’s participation requirements. Your school or organization registers a team, your advisor adds eligible participants, and you take the four contests. There is no application review where ACSL accepts a fixed percentage of applicants.
The selective part comes later. ACSL invites top-scoring students to its end-of-year online Finals. That means “acceptance rate” is not a particularly useful way to describe the regular competition. A better question is whether your scores are strong enough to qualify for the Finals in your division.
ACSL also has a substantial international participant base. The organization says that more than 7,000 students from 21 countries participated in its regular season in the previous year.
If you are comparing ACSL with more selective programming competitions, our guide to programming competitions for high school students gives you a broader view of how different competitions handle qualification and advancement.
What does ACSL cost, and what do you get for it?
The regular ACSL season is registered by teams rather than individual students.
For the current season, the first team in the Senior, Intermediate, Junior, or Classroom division costs $175. An additional team in the same division costs $150. The Elementary division costs $125 for the first team and $100 for each additional team.
The registration fee is paid by the advisor when the team is registered. A 5-score team can have up to ten students, while a 3-score team can have up to six, so the per-student cost depends on how many people are on the team.
The separate Summer Coding Challenge costs $20 per participant.
Outcomes and what they require
| Outcome | What it requires |
| Certificate of participation | Participation in the Summer Coding Challenge. ACSL says all Summer Coding Challenge participants receive a certificate. |
| Top-three Summer Challenge prize | Finishing among the top three participants in the Rookie or Veteran division of the Summer Coding Challenge. |
| ACSL Finals invitation | Strong enough regular-season scores to qualify for the invitation-only individual Finals. |
The regular season also has certificates for top-scoring individual students and teams in each U.S. state and each non-U.S. country based on cumulative scores after the fourth contest. Finals participants who place at the top of their divisions receive prizes and certificates.
What skills can you build through ACSL?
ACSL covers more than programming. Its regular-season contests test foundational computer science concepts alongside programming in the Junior, Intermediate, and Senior divisions.
Depending on your division and the contest, you can work on:
- Programming: Writing solutions in Python, Java, or C++
- Algorithmic thinking: Breaking a problem into steps that can be implemented
- Number systems: Understanding different ways computers represent numbers
- Recursive functions: Tracing and reasoning about recursive programs
- Boolean algebra: Working with logical expressions and operations
- Data structures: Understanding ways of organizing and manipulating data
- Digital electronics: Working with concepts related to digital systems
- Graph theory: Reasoning about relationships between connected objects
- Regular expressions: Understanding patterns used to describe strings
- Debugging: Finding and fixing problems in a program
- Time management: Working within fixed competition limits
The exact topics vary by division and contest. For example, the current Senior and Intermediate study materials include number systems, recursive functions, prefix and postfix notation, bit-string operations, LISP, Boolean algebra, data structures, finite-state automata and regular expressions, graph theory, digital electronics, and assembly language.
The programming component also gives you a chance to practice turning a problem description into working code. ACSL allows Python 3, Java, and C++ for its programming problems.
Who is ACSL the right fit for and who should look elsewhere?
ACSL can be a good fit if you like solving problems and want regular practice with computer science concepts. You can enter different divisions based on your age, grade, and experience, so you do not need to be an advanced programmer to find an appropriate regular-season division.
It can also work well if you enjoy measurable competition. You take defined tests, receive scores, build a cumulative record across four contests, and can qualify for an individual Finals competition based on your performance.
ACSL may be less useful if your main goal is to spend several months investigating one original computer science question and producing a research paper or substantial independent project. In that case, a mentored research experience can give you a different kind of academic experience. This guide to computer science research opportunities is a useful place to explore that route.
ACSL questions to know before you register
For the regular season, your school, club, or organization needs an advisor who registers the team. The advisor can be a teacher, parent, or another adult with computer science experience. The advisor then adds students to the team through the ACSL Leaderboard. You can only participate on one ACSL team, and after Contest #1 you cannot change teams.
No. ACSL requires students to complete the tests individually. Its current rules say that students cannot consult or copy code from websites, books, friends, or colleagues while completing the tests. Paper and pencil are allowed, but calculators, internet searches for code or solutions, and human assistance are not. HackerRank also uses plagiarism detection for programming submissions.
No. ACSL has several regular-season divisions with different levels of difficulty. The Intermediate division is designed for high school students with little or no programming experience as well as advanced junior high students, while the Classroom and Elementary divisions do not include programming problems.
A competition can help you practice problem solving and measure your performance, while a research project gives you time to investigate one question in greater depth. If you want to build that kind of sustained independent project with a mentor, explore the Horizon Academic Research Program.
Image source: Horizon Academic Research Program