It's the bedtime ritual many parents have to endure - being asked to read the same book for the umpteenth time.
But while the constant repetition might be mind-numbing for mum or dad, it is the best way for toddlers to learn new words, according to a study.
The findings suggest parents are wasting money spending a fortune on books when a small selection of favourites can achieve far better results.
Researchers visited a group of three-year-old children several times during the course of a week.
Half of them heard the same story back-to-back while the rest were read three different books. Both groups were exposed to six new words.
When they were tested a week later, the ones who heard the same story over and over again remembered an average of 3.6 new words. But those exposed to a variety of stories typically remembered only 2.6.
Dr Jessica Horst, from the University of Sussex, said: "Kids actually learn better when the information that they are not even trying to learn is repeated."
Dr Horst has already introduced the technique to her 19-month-old son.
"I read the same books to him. Sometimes, every single day he wants the same books," she said.
"We are showing that less is more, to a point. Obviously, the more times you read to a child and the more books you have will help them.
"But you don't need to go crazy and buy every single Thomas the Tank Engine book. Reading the same books over and over again helps."
One in three parents says they don't read to their children before putting them to bed.
But research suggests half an hour of story time every night can improve a young child's reading age by nearly two years in less than five months.