Pupils at about 400 Kenyan schools are trying to break the world record for having the most people reading aloud simultaneously from the same book.
They read from Attack of the Shidas about children from different Kenyan communities working together to protect their well from an alien invasion.
The event is meant to foster a culture of reading in the country, the organisers told the BBC.
The US currently holds the Guinness World Record set by 233,000 people.
It will take at least a week to work out whether they have been successful as they need to tally the number of pupils from across the country who participated.
Kenyan children's book author Muthoni Muchemi led the event with 1,700 students reading from her book at Hospital Hill Primary School in the capital, Nairobi.
Afterwards, she said she wanted to break the stereotype that Africans do not care for books.
"Growing up I would always hear that if you want to hide something from an African, put it in a book - and it was really upsetting to me," she told the BBC.
"I want to help change that perception and the first step is to re-introduce reading not just as important but enjoyable," she said.
"I have seen over the years that a lot of families don't have libraries in their homes but have they have big TVs. We need to get parents to understand that reading for pleasure with their children is an important part of brain development."
The 13- and 14-year-olds, dressed in grey and white uniforms, who chorused the words at Hospital Hill Primary School said they enjoyed the challenge.
"I enjoy reading because it teaches me about other people and places. It teaches me about the world," one girl said.
Another student said he thought Attack of the Shidas had important life lessons about working together and accepting people's differences.
It is not the first time Kenya has tried to break the record - last year 142,279 children read aloud in 360 schools.
This time, Ms Muchemi is more optimistic about the Storymoja National Read Aloud attempt.
But she says in the end it is about building confidence in children.
"If you master reading it means you've increased your vocabulary, you have good command of sentence structure, your facility with language is improved. It can't help but build your confidence," she said.
"Exposure to different stories makes you more confident in your place in the world because you no longer feel alone. It's served me very well because I grew up in a deep rural area."