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Many Class 8 students search for "Reaching the Age of Adolescence" and find a chapter their new textbook does not have. The topic has not gone away. It has moved, and the two NCERT versions cover slightly different ground. This guide sets out what each book says, works through the one calculation the chapter uses, and lists the questions students most often get wrong.
Where is adolescence in the 2026-27 NCERT books?
The new Class 8 science book, Curiosity for Grade 8, has 13 chapters, and none of them is about adolescence. The topic now sits in Class 7: Chapter 6 of Curiosity for Grade 7, "Adolescence: A Stage of Growth and Change". The older Class 8 Science chapter "Reaching the Age of Adolescence" (2024-25 reprint) is still on the NCERT site. Some schools may still use it, so check with your teacher which version your exam follows.
What counts as adolescence?
The Class 7 book says adolescence usually starts around age 10 and can continue to 19. The World Health Organization uses the same range: "the phase of life between childhood and adulthood, from ages 10 to 19". Puberty is the part of adolescence in which the body becomes capable of reproduction.
Both NCERT books list the same visible changes:
A growth spurt in height, and changes in body shape.
A deeper or hoarse voice as the voice box (larynx) grows. In boys it can show as the Adam's apple.
Hair in the armpits and pubic region, and facial hair in boys.
More active sweat and oil glands, which is why acne is common.
Breast development in girls, and the start of the menstrual cycle.
Changes like facial hair, voice change and breast development are called secondary sexual characteristics: they help tell male from female but are not directly part of reproduction.
What causes these changes?
Hormones. The older Class 8 chapter goes further than the Class 7 one. It explains that hormones come from endocrine (ductless) glands, which release them straight into the blood. At puberty the testes release testosterone and the ovaries release oestrogen, and both are controlled by hormones from the pituitary gland. The same chapter covers thyroxine (thyroid), insulin (pancreas) and adrenaline (adrenals), and explains that sex is decided by the father's sperm: an X-carrying sperm gives a girl (XX) and a Y-carrying sperm gives a boy (XY). That is why the book calls blaming the mother "totally unjustified".
On menstruation, the Class 7 book says a cycle usually repeats every 28 to 30 days, that healthy cycles can range from 21 to 35 days, and that bleeding usually lasts three to seven days. It calls isolating girls during periods a myth with no scientific basis.
How do you use the growth table? A worked example
The older Class 8 chapter has a table giving the average percentage of full adult height reached at each age. Two rows: at age 9, boys have reached 75%; at age 11, girls have reached 88%.
The formula is:
Likely full height = present height ÷ (% reached at this age) × 100
Example 1 (from the book): a 9-year-old boy is 120 cm tall. Full height = 120 ÷ 75 × 100 = 160 cm.
Example 2: an 11-year-old girl is 140 cm tall. Full height = 140 ÷ 88 × 100 = 159.1 cm (to one decimal place).
Two warnings. First, the book calls these figures "only representative", so this is an exam exercise, not a prediction. Second, the common slip is to multiply by the percentage (120 × 0.75 = 90 cm), which gives a height smaller than the child already is. If your answer is shorter than the present height, you have divided the wrong way.
Which questions do students get wrong?
Confusing adolescence and puberty. Adolescence is the whole stage; puberty is the change to reproductive maturity within it.
Assuming one timetable for everyone. Both books say the age and pace of these changes differ between people, so "late" or "early" is usually normal.
Mixing up glands. Sweat and oil glands use ducts; endocrine glands do not.
Getting sex determination backwards. The egg always carries an X. The sperm decides.
How should parents and students handle the non-exam side?
The Class 7 book spends real space on nutrition (calcium, protein and iron), hygiene, exercise, safe social media use and saying no to tobacco, alcohol and drugs. It lists the National De-addiction Helpline, 14446. Sleep matters too; our guide on teen sleep for parents covers it.
Adolescence can also bring strong emotions and mood swings, which the book treats as normal. If worry, low mood or stress lasts for weeks or gets in the way of school, talk to a doctor or counsellor. In India, Tele MANAS, the government's free mental health helpline, is on 14416 or 1-800-891-4416.
A short revision routine
Read the Class 7 chapter once, then the hormone and sex-determination sections of the older Class 8 chapter if your school uses it.
Close the book and write the list of changes from memory, sorting them into "boys", "girls" and "both", as the Class 7 exercises ask.
Do the growth-table calculation for two ages, and check the answer is taller than the present height.
Draw the endocrine glands from memory and label each with its hormone.
If a term like "endocrine" or "secondary sexual characteristic" still feels vague, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, so you can read a short explanation and then return to the textbook.
This week, ask your science teacher which of the two NCERT chapters your exam follows, and revise from that one.
