How to get an A* in IGCSE Chemistry: why students who understand still get a C

In IGCSE Chemistry (0620) Extended, June 2026, option 22/42/62, a C needed 80 of 200 weighted marks (40%) and an A* needed 169 (about 85%). The gap is real, but not all of it is missing knowledge. Many of those marks are lost on questions the student could answer, written in a way the examiner cannot credit.

Plenty of tutors explain the chemistry well. Without practice against the mark scheme, those marks do not come back however many more hours of content are added.

Cambridge publishes grade thresholds every series. Paper 2 (multiple choice, 30%), Paper 4 (written, 50%) and Paper 6 or 5 (practical, 20%) are weighted to a total of 200 and compared with the thresholds for that option.

June 2026, option 22/42/62: A* 169 · A 139 · B 109 · C 80. In November 2025 the same option's A* was 153. Thresholds moved by up to 16 marks between series as papers got harder or easier, so there is no fixed "percentage for an A*".

Enter marks for each paper below. It starts on a script that just makes a C; see how much more the next grade needs.

Many tutors are genuinely strong at chemistry; some are recent engineering or medical graduates with excellent results who explain things very clearly. But a tutor who has never taught IGCSE or read a Cambridge mark scheme can teach a student to know the chemistry without teaching them to score, because the rules for awarding marks sit in documents few people open.

Signs a parent can spot: teaching from a Thai school textbook or their own notes, no past papers marked point by point, unsure whether your child sits 0620 or 4CH1, Core or Extended, and skipping practical questions as easy.

That last one matters more than it seems. Paper 6 is 20% of the grade, and students who have not practised it mix up basic terms such as reliable and accurate.

Tick what your child's tutor already does. The point is not to judge anyone but to see where the gap is.

No working: the right method with one slip. A bare final answer scores 0; with working shown, the examiner can give partial credit.

The wrong command word: asked to Describe (what is seen), the student Explains (why). Every word of chemistry is correct, and it scores 0.

One wrong word: intermolecular forces for an ionic compound costs the whole mark. Examiners mark what is written, not what was meant.

Practical questions: the student knows the results should be better but writes about accuracy when the question asks about reliability.

Guess each answer's score before you see the marking. This student knows every answer and still loses almost every mark.

Boom, who teaches at Boom-Tutor, on the student who changed the way Boom teaches:

"When I first started tutoring IGCSE Chemistry, I made exactly this mistake. One of my students understood chemistry more deeply than many A* students I knew. This student asked questions that sent me back to the textbook. The result was a B."

"I went through the paper question by question. There was nothing this student didn't know. The marks went on Explain questions answered as Describe, on calculations with skipped steps, and on observations written too vaguely. That was my fault, not the student's. I had taught the chemistry, not how to write what the examiner looks for."

"Since then, every topic I teach ends with practice in answering to the marking points, and later students who learned that way started getting A/A*."

Understand the content first, then practise writing English answers to each command word in every topic, not just past papers in the final month.

Do past papers under timed conditions, mark them point by point against the mark scheme, and keep every missing word in one notebook. The marks lost again and again are usually the same handful of words.

Take Paper 6 (or Paper 5) as seriously as Paper 4: 20% of the grade is there.

Show every step and give units every time, even when you can do it in your head.

Every topic in the course ends with exam-style questions practised against the marking points, uses interactives so students see the idea instead of memorising it, and has on-screen experiments for students who have never been in a lab, to prepare for Paper 6-style questions.

The IGCSE Chemistry self-learn course is ฿4,900, paid once, with access until the exam. The platform is expected to open around December 2026. To find where your child is losing marks, start with the free diagnostic test, or book a 30-minute chat with Boom.