Q: A Class 12 student's Python program 'works' but crashes on the boundary case. How do you teach debugging?

First rule: don't guess, print. Add print statements or use a debugger to trace values through the failing case. Second rule: read the error message end to end — Python's tracebacks tell you exactly what went wrong and where. Third: write the smallest test case that reproduces it. Debugging is a skill you build by not skipping steps, and students who learn it in Class 12 don't struggle in college.

Q: Explain a stack using a real-world analogy and one Python implementation.

Analogy: a pile of plates in the canteen — you can only add or remove from the top. Last in, first out. Python: use a list, .append() to push, .pop() to pop, [-1] to peek. Alternative: collections.deque for better performance in large-scale cases. Draw the stack on the board as boxes stacking upward as you push. That visual makes recursion click later.

Q: Which Class 12 CS topic do students routinely struggle with?

File handling — students memorise open/close but never understand modes ('r', 'w', 'a', 'r+'). I spend one lesson only on modes with a physical file cabinet analogy, then move to actual code. Also SQL joins — INNER, LEFT, RIGHT — students confuse them because they've never seen a Venn diagram of the result sets. Fix that with one slide.

Q: A student writes better code than you sometimes. How do you handle it?

Ask them to walk the class through it on the board. Publicly acknowledge that their solution is cleaner. Assign them stretch problems from CodeChef or NCERT-supplementary. In CS, the moment you pretend to know more than a student who clearly knows more, you lose the class. Own the gap and grow with them.

Q: Half the class has laptops at home, half don't. How do you set homework?

Never assume access. Homework is always pen-and-paper — write out the code, trace values, predict output. Lab time is for actual coding, and lab is scheduled twice a week for the have-nots to catch up. Assigning laptop-required work at home widens the gap; a Class 12 CS teacher who does that fails half the class silently.

Q: A parent wants their child moved out of CS because 'coding isn't important for their career path'. Response?

Listen, then share what CS teaches beyond coding — logical decomposition, precise thinking, debugging as a mindset. If after that the parent still wants a change, escalate to the coordinator. Don't fight the parent, but do give them the fuller picture — many parents underestimate CS because their own generation didn't have it in school.

Q: How do you keep Class 11 excited when the syllabus starts with Python basics they've done in Class 9?

Skip the recap, jump straight to a project — build a small text-based adventure game in Week 1. Basics get revised in the doing, not in review lessons. Nothing kills a Class 11 CS batch faster than three weeks of 'print statements'.

Question 1

Write a Python function to check whether a string is a palindrome — on the whiteboard, no editor.

Accepted Answer

def is_palindrome(s): s = s.lower(); return s == s[::-1]. Then talk it through: lowercase to make it case-insensitive, slice with step -1 to reverse, compare. Mention edge cases you're skipping — non-alphanumeric characters, unicode — and how you'd handle them if needed. Board panels test whether you code without autocomplete, not whether you produce the cleverest solution.

Question 2

Explain the difference between a list and a tuple to a Class 11 student — one whiteboard, one minute.

Accepted Answer

Both are ordered sequences. List is mutable — you can append, remove, modify. Tuple is immutable — once created, no changes. Use a tuple when the data shouldn't change (coordinates, RGB colours, database row); use a list when it will (a shopping cart). Tuples are also slightly faster and can be dictionary keys; lists can't. Give one example of each on the board.

Question 3

SQL: write a query that gives the second-highest salary in an employees table.

Accepted Answer

SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees); — simple subquery approach, works everywhere. Alternative with LIMIT/OFFSET (SELECT DISTINCT salary FROM employees ORDER BY salary DESC LIMIT 1 OFFSET 1) is cleaner but doesn't handle ties well. Show both, explain the trade-off. Class 12 SQL is 8–10 marks in the board; this exact pattern shows up often.

Question 4

A Class 12 student's Python program 'works' but crashes on the boundary case. How do you teach debugging?

Accepted Answer

First rule: don't guess, print. Add print statements or use a debugger to trace values through the failing case. Second rule: read the error message end to end — Python's tracebacks tell you exactly what went wrong and where. Third: write the smallest test case that reproduces it. Debugging is a skill you build by not skipping steps, and students who learn it in Class 12 don't struggle in college.

Question 5

Explain a stack using a real-world analogy and one Python implementation.

Accepted Answer

Analogy: a pile of plates in the canteen — you can only add or remove from the top. Last in, first out. Python: use a list, .append() to push, .pop() to pop, [-1] to peek. Alternative: collections.deque for better performance in large-scale cases. Draw the stack on the board as boxes stacking upward as you push. That visual makes recursion click later.

Question 6

Which Class 12 CS topic do students routinely struggle with?

Accepted Answer

File handling — students memorise open/close but never understand modes ('r', 'w', 'a', 'r+'). I spend one lesson only on modes with a physical file cabinet analogy, then move to actual code. Also SQL joins — INNER, LEFT, RIGHT — students confuse them because they've never seen a Venn diagram of the result sets. Fix that with one slide.

Question 7

A student writes better code than you sometimes. How do you handle it?

Accepted Answer

Ask them to walk the class through it on the board. Publicly acknowledge that their solution is cleaner. Assign them stretch problems from CodeChef or NCERT-supplementary. In CS, the moment you pretend to know more than a student who clearly knows more, you lose the class. Own the gap and grow with them.

Question 8

Half the class has laptops at home, half don't. How do you set homework?

Accepted Answer

Never assume access. Homework is always pen-and-paper — write out the code, trace values, predict output. Lab time is for actual coding, and lab is scheduled twice a week for the have-nots to catch up. Assigning laptop-required work at home widens the gap; a Class 12 CS teacher who does that fails half the class silently.

Question 9

A parent wants their child moved out of CS because 'coding isn't important for their career path'. Response?

Accepted Answer

Listen, then share what CS teaches beyond coding — logical decomposition, precise thinking, debugging as a mindset. If after that the parent still wants a change, escalate to the coordinator. Don't fight the parent, but do give them the fuller picture — many parents underestimate CS because their own generation didn't have it in school.

Question 10

How do you keep Class 11 excited when the syllabus starts with Python basics they've done in Class 9?

Accepted Answer

Skip the recap, jump straight to a project — build a small text-based adventure game in Week 1. Basics get revised in the doing, not in review lessons. Nothing kills a Class 11 CS batch faster than three weeks of 'print statements'.

Question 11

Why teaching and not industry?

Accepted Answer

I worked in industry for X years and realised the highest-leverage thing I can do with my skills is teach 40 Class 12 students who'll go into industry. Explaining well is a rarer skill than coding; both matter, but only one scales this way. Teaching is a legitimate technical career, not a fallback.

Question 12

How do you keep your CS skills current?

Accepted Answer

One personal project a quarter (small, shipped), one CS book a year, and I follow CBSE's syllabus updates plus one industry blog to know what to add outside the textbook. A CS teacher who hasn't written a line of code in five years teaches obsolete Python — that's a real risk in the subject.

Question 13

Salary expectation?

Accepted Answer

For a PGT Computer Science role at your school, ₹X–Y lakh CTC. Open to discussing based on batch load and any project-mentoring outside class hours.

PGT Computer Science interview questions and answers (2026)

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What this interview actually looks like

Questions with model answers

Q1Write a Python function to check whether a string is a palindrome — on the whiteboard, no editor.

Q2Explain the difference between a list and a tuple to a Class 11 student — one whiteboard, one minute.

Q3SQL: write a query that gives the second-highest salary in an employees table.

Q4A Class 12 student's Python program 'works' but crashes on the boundary case. How do you teach debugging?

Q5Explain a stack using a real-world analogy and one Python implementation.

Q6Which Class 12 CS topic do students routinely struggle with?

A 15-minute demo you can teach on Monday

Ask them back — questions for the interviewer

Ready to apply?

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