What it is
The International Science Olympiad (ISO) is the science olympiad run by the Science Olympiad Foundation (SOF). Until the 2025–26 session it was called the National Science Olympiad, or NSO, and many parents, teachers and books still use that name. From 2026–27 SOF calls it SOF ISO; it is the same olympiad, still written in school and still in two levels.
The Level 1 paper has three sections for most classes:
- Logical Reasoning: verbal and non-verbal reasoning, such as series, analogies, classification and pattern questions.
- Science: the science of the class syllabus, from living and non-living things in the junior classes to matter, force, light, the human body and the environment later on.
- Achievers Section: five higher-order questions on the science syllabus, worth more marks each.
Classes 11 and 12 write a different paper: Physics and Chemistry, then Mathematics or Biology, then the Achievers Section.
| Classes | First section | Second section | Achievers Section | Total |
|---|---|---|---|---|
| 1–4 | Logical Reasoning: 5 | Science: 25 | 5 | 35 questions, 40 marks |
| 5–10 | Logical Reasoning: 10 | Science: 35 | 5 | 50 questions, 60 marks |
| 11–12 | Physics and Chemistry: 25 | Mathematics or Biology: 20 | 5 | 50 questions, 60 marks |
All questions are multiple choice. The paper lasts one hour and is in English.
Who can take it
Students from Class 1 to Class 12 in schools registered with SOF, each writing the paper for their own class. There is no Level 2 for Classes 1 and 2, so for them Level 1 is the whole olympiad.
SOF does not accept individual entries. A family whose school does not take part can pass SOF’s details to the school; any school can ask SOF for its prospectus.
How it works
The first level is organised in each participating school, during school hours. A teacher acts as coordinator: they register the students, receive the roll numbers and conduct the paper on the date the school chose from SOF’s list. Registrations must reach SOF at least 30 days before that date, and SOF asks for a minimum number of students per school.
Students in Classes 3–12 move to Level 2 if they meet any one of three conditions set out on SOF’s rankings page:
- they are in the top 5% of their class in Level 1;
- they are among the top 25 rank holders of their class in their zone; or
- they top their class in a school where at least 10 students from that class wrote the paper, scoring at least 50%.
Level 2 drops the reasoning section. Classes 3–10 answer a longer science section plus the Achievers Section, and Classes 11–12 keep their physics, chemistry and maths or biology sections. SOF’s syllabus pages say Level 2 questions come from the current class syllabus only.
SOF publishes international, zonal and school ranks for each class, and describes medals, certificates and other awards for top rank holders, along with recognition for schools and teachers. The full list for the year is on the official site. If Level 2 cannot be held, Level 1 results are treated as final.
When it happens
Level 1 is usually held between late October and early December, on whichever of SOF’s dates the school chose. Level 2 usually follows in February. The exact dates, and the last date for the school to register, are on the official SOF page. The olympiad calendar puts this alongside the other olympiads of the year.
How to prepare
Revise two years of science, not one. For Level 1, SOF’s syllabus pages say about 60% of questions come from the current class and 40% from the class before. A Class 8 student should therefore revise the Class 7 science textbook as well as this year’s chapters, starting with the topics they found hardest at the time.
Read the question, then the options. Science olympiad questions often describe an experiment or a situation and ask what will happen. Reading the whole stem slowly, then ruling out options that contradict it, saves more marks than memorising definitions.
Use diagrams. Many questions show a labelled figure: a plant cell, a circuit, a ray of light through a lens. Drawing these from memory a few times is good practice at any age.
Don’t ignore reasoning in the junior classes. Up to Class 10 the paper opens with a reasoning section. It is small for younger children (5 questions) and grows to 10 from Class 5; short daily puzzles are enough.
Plan six to eight weeks. Two or three sessions a week, each ending with a handful of SOF sample questions, is a steady pace for Classes 5–10. Younger children need less. For Classes 11–12, olympiad work should sit inside regular board revision, not beside it. The science prep guide has more by class.
Where daily practice fits
Ado’s free daily quiz has 8 questions a day, including a 60-second sprint, across science, maths, English, GK and reasoning, plus social studies. Doing it every day builds the habit of reading a question carefully and answering in good time, in the same subjects this olympiad covers. Each student is ranked only against students the same age, through the Ado Rank, which builds from their three strongest subjects and never resets.
Good to know
Searching for “SOF NSO” still brings up older pages, and some books are still printed under the old name. Sample papers labelled NSO are the same olympiad’s papers from earlier years. Other science olympiads written in school include SilverZone’s International Olympiad of Science and Unified Council’s NSTSE.