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How would you design a bookshelf for children?

A Product Design Question for Product Management Interviews

by Malena Mesarina, Co-founder, StellarPeers

StellarPeers is a community platform that helps professionals prepare for interviews. We think the best way to prepare, is to work through questions and practice mock interviews as much as possible. We meet weekly to discuss product management interview questions on product design, product launch, strategy, marketing, pricing, and others. Last week, we worked on a product design interview question.

What is this question about?

The core responsibility of a product manager is to drive product vision, design and development. A business decides to make a product because it has identified a real customer need for which the customer is willing to pay. It is the role of the product manager to identify customer needs and drive the design and development of products that meet those needs.

This product design interview question tests whether you understand the process of going from customer needs to product development. This process should involve defining who the customer is and what they want to accomplish; defining multiple use case scenarios in which the customer does activities that are related to your product; and prioritizing what to build.

What is the interviewer looking for?

The interviewer is evaluating you on the following:

  • Do you provide keen insights about the customer and their needs?
  • Are you able to provide multiple and diverse use case scenarios?
  • Is your answer structured and logical, or do you go off on a tangent?
  • Do you go beyond generalities in your solutions and provide detailed descriptions?
  • Can you provide ideas that no other candidate has mentioned?
  • Are you confident and sound credible? Would engineers and product people follow your lead?

How to structure your answer?

One way to guide your answer is by following the steps of the CIRCLES Method™ by Lewis C. Lin. A detailed description of this method is in the book Decode and Conquer. This method is very useful in helping you think and answer in an organized and exhaustive way.

The steps of this method are:

C — Clarify. Ask questions to clarify what you are unsure of or confirm/disconfirm assumptions.

I — Identify the users/customers as personas like food lovers, soccer moms, etc.

R — Report on their needs (use cases). A use case is an activity that a user would like to do relative to your product.

C — Cut through and prioritize the use cases based on some attributes (revenue, customer benefit, complexity).

L — List solutions.

E — Evaluate the tradeoffs of your solutions.

S — Summarize:

  • State which solution you would recommend.
  • Recap what the solution does and why it is beneficial.
  • Explain why you prefer this solution.

How to quickly think of several use cases?

Use cases are at the heart of this question. Without use cases, you will have nothing to solve for. Because the interview is a conversation, you can’t ask for too much time to think about use cases. You can ask for at most one minute. This time constraint can cause anxiety because you need to think fast and then articulate your ideas almost simultaneously.

Sometimes we don’t have enough ideas on paper after one minute, or we are afraid of being silent and start answering immediately saying whatever comes to mind. The result is that we end up blurting attributes of a product or go straight to listing solutions without realizing that we haven’t described what kind of need or use case we are solving for.

Therefore, it is important to have a strategy or a method that triggers ideas for use cases fast. It is also important to articulate the use cases in a sentence that describes the user doing an action instead of just listing attributes of a solution.

Below are three strategies that can help spark ideas for use cases. Use the method or methods that you think will work best for you.

Method 1: Ask yourself the 5Ws

Start by asking yourself the 5Ws, in the order that is most useful.

  • Who is the user?
  • Why do they need to use this product?
  • What do they want to solve or do by using the product?
  • When will they be using the product?
  • Where will they be using the product?

By asking these questions to yourself, you may discover multiple types of users and use cases with different needs.

Method 2: Use word associations

Write down keywords from the question and circle them. Then think of other words or verbs that you associate with those keywords and connect them graphically with a line. If you have time, you can go one more level and connect other words to the previous words. As you are doing this, ideas for use cases will occur to you. Write down these ideas as bullet points using short sentences, if you have time.

Method 3: Use SCAMPER

SCAMPER is a technique to generate multiple and different ideas based on 7 actions:

S — Substitute something.

C — Combine it with something else.

A — Adapt something to it.

M — Magnify or Modify it.

P — Put it to another use.

E — Eliminate something.

R — Reverse or Rearrange it.

The objective of SCAMPER is to apply the actions to an existing product or service in order to generate new ideas for its usage. You could use scamper to think of use cases. To learn more about SCAMPER, read Creative Problem Solving with SCAMPER.

Common Mistakes

People get nervous when answering this question because they have to think on their feet. Below are some common mistakes people make:

  • Forgetting to ask clarifying questions.
  • Describing use cases as attributes that a solution should have instead of using sentences that describe what activities or tasks the user may do related to the product. For example, for the question “How would you design a bookshelf for children?”, saying something like, “the bookshelf should be durable, without sharp edges, and not too tall” is only listing attributes. The interviewer has forgotten to describe the use case that calls for those attributes. A better answer would be, “children have a tendency to stumble and fall, so the bookshelf should not have sharp edges.” Remember, the interviewer is looking to see if you think like a PM, and a PM doesn’t come up with solutions without knowing if the solution is meeting a critical use case.
  • Going straight to solutions without explaining what use cases those solutions are supporting.
  • Mentioning various use cases but forgetting in which order they talked about them.
  • Not clearly explaining what criteria they are using to prioritize use cases.
  • Not pushing themselves to think of original ideas, and ending up mentioning the same use cases or solutions that others have mentioned.
  • Forgetting to go into details about how to build a solution.
  • Forgetting to wrap up and provide a recommendation.

Answer Example

INTERVIEWEE: Could you tell me what the desired objective is for the design?

INTERVIEWER: We would like to design a bookshelf that stands out for its innovation, not just the usual usage of placing books or things on it.

INTERVIEWEE: And where would the bookshelf be used? The obvious place is in family households but I can also see schools, children’s hospitals or any institution that deals with children using bookshelves too.

INTERVIEWER: Let’s say it is for family households.

INTERVIEWEE: Okay. And what is the age or age range of the children we are designing the bookshelf for?

INTERVIEWER: Between the ages of 5 and 10.

INTERVIEWEE: Okay. The way I will go about answering this question is to first understand who the user or users are and what activities they would like to do relative to bookshelves. There may be some activities that no bookshelf serves today which could lead to innovative designs. After selecting some use cases, I will describe solutions and how to build them. Then I will wrap up with my final recommendation.

INTERVIEWER: Sounds good, please continue.


Identifying Users

Parents are the most likely buyers of bookshelves for their children. Since the goal is to design an innovative bookshelf, I think the types of families buying such a bookshelf would be families with high disposable incomes. High income families are likely to favor design over utility. Children will also use the bookshelf, so we will need to keep their behavior and needs in mind.

Listing Use Cases

Now I would like to think about different use cases, that is activities parents and children like to do that are related to a bookshelf. This will help spark new ideas for creating innovative designs for bookshelves. Could I take a minute to write down some preliminary ideas about possible use cases?


The interviewee writes down on a piece of paper words and ideas using the brainstorming methods mentioned above. The interviewee will use the output of this creative process to think of different use cases.

Brainstorming notes

INTERVIEWEE: Okay, I can think of the following use cases involving a bookshelf:

  1. Parents that borrow books from their local library may need reminders to return them (from word association: “parents—borrow books”).
  2. Parents may need help with keeping track of which books they’ve already bought to not mistakenly buy them again (from word association: “parents—buy books”).
  3. Since children grow up quickly, a height adjustable bookshelf would be useful (from word association: “bookshelf—height”).
  4. A bookshelf could be used as a desk if it had a top (from word association: “bookshelf—table”).
  5. Children like to use furniture to make forts, maybe the bookshelf could be transformed into one (from word association : “children—forts”).
  6. Parents may like to get recommendations on which book to read their children next (from word association: “parent—read stories”).
  7. The bookshelf could read a story to the children before they go to bed instead of the parent (from word association: “parent—read books”).
  8. Children love songs, so maybe the bookshelf could play a song that fits the story (from word association: “parent—read books”).
  9. The bookshelf could become a drum by creating a cover for the bookshelf and allowing different parts to produce different pitches (from combining word association: “bookshelf—dust” and SCAMPER Put it to another use: “drum instrument” and thinking of cover that protects from dust but also can make sounds).
  10. It is always a pain to dust bookshelves, so perhaps the bookshelf could be self-dusting (from word association: “bookshelf—dust”).
  11. Embed a display into a bookshelf to provide a summary and information about each book on the shelf (from SCAMPER Adapt: “embed a display to summarize books”).
  12. People forget to put books back on a bookshelf, so maybe the bookshelf could weep as though it misses the books and ask for the books to be put back; a “weeping bookshelf” (from word association: “parent—put books back”).
  13. Children could use a long single shelf of a bookshelf for fun as a ‘seesaw’ (from word association: “children—playground”).

Prioritizing Use Cases

There are a lot of use cases we could design for but we need to prioritize those that meet the innovation design goal and provide a benefit to the customer. To make this selection, I would prioritize a use case based on whether a solution could be highly original; whether it targets children; whether it is easy to build; and whether it is a frequent use case.

Of all the use cases, I think the one that would spark an original design is the “Seesaw” bookshelf, which children could use for shelving books and for fun. It is not complex to make, and I think that children would use it often, because having a seesaw is like having a playground available 24x7.

The second best use case is the “Drum bookshelf.” It is an innovative concept and children would play with it. The concept is not difficult to build but I think children would try it a few times and then get bored with it.

My third favorite use case would be the “Weeping bookshelf.” A smart bookshelf that reminds people to put books back would be innovative and useful because it is a frequent scenario. But it is not children oriented and would be very complex to make because it would require technology to identify which books are not on the shelf, which is hard to do. The best technology today is radio-frequency identification (RFID), but even with this technology it would be hard to read RFID tags from books that are so close together, and it would be a logistical headache to add tags to the books.

Therefore, I would choose the Seesaw bookshelf use case as the best one to target. What do you think?

INTERVIEWER: It makes sense, so how would you implement a solution for it?


Listing Solutions

To design a bookshelf that also functions as a seesaw, I would consider the following:

  • The bookshelf would consist of one long horizontal shelf placed on top of a standing pole that would serve as a middle hinge for the shelf.
  • The material of the shelf would need to be strong enough to hold the books and support the weight of a child, so probably thick wood or metal.
  • On each side of the top part of the shelf, there should be handles for children to hold on to.
  • Since the seesaw goes up and down, I would split the shelf into two sides: right and left, with a plate in the middle that stops books from going from one end to the other. This is to protect the books from sliding from one end to the other and to prevent too much noise.
  • If the weight of the books on one end is equivalent to the child on the other end, than it would be easy for the child to go up and down. If there is a disparity in weight, a scale could be integrated to calculate how much or less additional weight there needs to be on the other side. For example, if the scale calculates that a child needs extra weight at the opposite end, then the child could add more books to that end and the scale would make a sound when the weight is correct.
  • A more sophisticated solution could include an electronic system that would automatically sense the weight on both sides and control the speed going up and down according to how fast the child wants to go.


I can see three versions of the solution: the basic version with no scale, the intermediate version with the scale, and the advanced version with the electric system. And offer versions with various colors and patterns that appeal to children.

I would first launch the product with the basic seesaw bookshelf, to see if the idea appeals to customers. If that is successful, then I would test the appeal of the intermediate and advanced versions by testing the products with the customers that liked the basic version.

In summary, I identified parents with high disposable incomes as the likeliest buyers of a new innovative bookshelf. I listed several use cases, and chose the seesaw bookshelf as the best option given that it would call for an innovative design, appeals to children, and was not too complex to make. I proposed three solutions: one basic, one intermediate and one advanced; and recommended starting with the basic version to test the appeal of the idea first. As an only child, I would have loved a bookshelf like this, because I had no siblings to play with, so I am excited about this design.


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