SOF ISO vs SilverZone iOS: which science olympiad to pick

If your child is in Class 6, 7 or 8 and the school has mentioned a science olympiad, the two names most likely to come up are SOF ISO — the International Science Olympiad, which the Science Olympiad Foundation renamed from NSO for this session — and SilverZone iOS, the International Olympiad of Science. Both of their registration windows involve the same date, 30 September 2026, and it means two different things. One is a date SilverZone publishes outright. The other is not a date SOF publishes at all; it is a subtraction from a rule, and it only applies if your school has picked one particular sitting. That difference is the part worth getting straight first, because it changes who you need to talk to.

Do these papers change between Class 6, 7 and 8?

Neither of them does, and that is worth saying plainly because the equivalent maths papers do not behave the same way. SOF ISO is 50 questions for 60 marks in 60 minutes at all three classes, split identically every time: Logical Reasoning 10 questions, Science 35 questions, and an Achievers Section of 5 questions worth 3 marks each. SilverZone iOS is 35 questions for 100 marks in 40 minutes at all three classes, and its split also holds: 23 questions across the named science sections at 2.5 marks each, 7 Reasoning and Aptitude questions at 3 marks, and 5 Scholar’s Zone questions at 4.3 marks. Only the chapter names behind those sections move up a year. This is the opposite of SilverZone iOM, the maths paper, which shifts 5 questions out of its named syllabus sections between Class 6 and Class 7. If you have read that comparison and assumed science works the same way, it does not — the science paper you prepare for at Class 6 is structurally the paper your child meets at Class 8.

How much of each paper is actually science?

More of ISO than of iOS, and the gap is larger than the section names suggest. On SOF ISO, 35 of the 50 questions come straight from the named science sections, and the 5 Achievers questions are science too — harder science, at 3 marks each. That leaves Logical Reasoning as the only non-science block: 10 questions and 10 marks, a sixth of the paper. On SilverZone iOS, the named science sections are 23 questions and 57.5 of the 100 marks, so a shade over two-fifths of the iOS paper sits outside the science chapters your child has revised — 21 marks of Reasoning and Aptitude and 21.5 marks of Scholar’s Zone. A child who knows the chapters cold and has never practised non-verbal reasoning will feel that difference on iOS and barely notice it on ISO.

Which paper gives a child more time to think?

SOF ISO, by a small margin, and it is the opposite of how the two papers read on paper. “35 questions in 40 minutes” sounds calmer than “50 questions in 60 minutes”, but the arithmetic runs the other way: 40 minutes across 35 questions is about 69 seconds each, and 60 minutes across 50 questions is about 72. The real difference is not pace but what a mistake costs. On ISO most questions are worth 1 mark of 60, so a dropped one costs under 2 per cent of the paper, and even an Achievers question is 3 marks of 60. On iOS every named-section question is 2.5 marks of 100 and a Scholar’s Zone question is 4.3 — so a single stall there costs more than twice what it does on ISO. iOS rewards accuracy; ISO rewards steady coverage.

When does registration for each one close?

Both answers involve 30 September 2026, and they are not the same kind of date. SilverZone publishes one registration date covering every paper it runs — 30 September 2026 — on a schedule it heads “Tentative Examination Schedule for the year 2026-27”, so treat it as the body’s own stated date rather than a final one. SOF publishes no closing date anywhere; it publishes a rule, in its own words: “Schools may send registrations by 30 days before the chosen date of each exam.” Applied to ISO’s three sittings, that gives 30 September 2026 if your school picks the 30 October sitting, 20 October if your school picks 19 November, and 3 November if your school picks 3 December. The 30 September figure is only a deadline for families whose school has chosen the October date, and SOF adds that once a school has chosen, “Change of date is not permitted”.

Both of those dates bind your school rather than you, so the single most useful thing a parent can do this week is ask the coordinator one question: which sitting have you picked for this paper? Until that is answered the SOF figure cannot be worked out at all. SilverZone also runs a public individual registration form at r.silverzone.org, which its own page describes as being “for individual registrations only. This is not a school registration link.” We have not been able to confirm which papers that form offers, what it costs, or what closing date applies to it — the 30 September date above is the school route’s — so ask SilverZone directly before counting on it.

What if your school offers neither paper?

Then neither of these two is available to you, because both are entered through a school — and there are still several science papers a family can register for without one. CREST Olympiads registers a student directly with no school involvement at all, and it is the simplest of the routes. Humming Bird Education registers a family directly for Classes 1 to 12 at ₹150 a subject, and you pick which of its two dates your child sits at the moment you register. Unified Council runs both routes, and its online sitting for NSTSE happens on a later date than the school one rather than the same day — though NSTSE is a talent search rather than a pure science paper, and covers maths as well as science. Indian Talent Olympiad runs a separate individual online route with its own dates and its own deadline. None of CREST, Humming Bird or Unified Council publishes a registration cutoff at all — that is a checked fact rather than a gap in our research, and it means early is better than late rather than that the door stays open.

Which one should a Class 6, 7 or 8 child take?

Where the school offers both and there is room for two exam days, the honest split is this. A child whose science is strong but who has never done timed non-verbal reasoning should know that more than two-fifths of the iOS paper sits outside the chapters — reasoning there is a subject to practise, not a warm-up to skim. A child who wants the widest possible coverage of the science itself will get more out of ISO, where 40 of the 50 questions are science. And a child who is accurate but slow to commit is better served by ISO, where one dropped question costs under 2 per cent of the paper. Neither exam is a harder version of the other, and neither is wasted preparation for the other. Most often the school has already decided, in which case the question is not which to pick but which sitting they chose.

Can a child prepare once for both papers?

Largely, yes. The section weights and the registration routes differ; the science underneath does not. Both papers are set on the current NCERT Curiosity book for your child’s class, asked in an olympiad shape, and SOF states for ISO that a Class 7 paper draws 60 per cent of its questions from Class 7 and 40 per cent from Class 6 — so last year’s chapters stay in scope either way. A child fluent in this year’s chapters who has met enough olympiad-pattern questions to recognise the shapes is prepared for both. The honest extra work for the second exam is section practice — reasoning for iOS, pace for ISO — rather than new syllabus.

That second half is what a workbook struggles with, because a book cannot generate a question it does not already contain. OlympAI generates olympiad-pattern practice for Classes 6 to 8 across all five subjects — English, Hindi, Maths, Science and Social Science — with a daily practice cap of 20 questions per subject on the free tier and 200 per subject on a paid plan.