The publisher of Philip Pullman's Whitbread award-winning children's book, The Amber Spyglass, has created a multimillion-pound fortune for the founder of The Book People by paying up to £15m for a 15% stake in the direct selling business.

Nasdaq-listed Scholastic, which claims to be the world's largest children's book publisher and counts Philip Pullman's Dark Materials trilogy among its titles, yesterday announced a wide-ranging strategic agreement with the British company, whose book sales are a regular feature in offices, schools and factories.

The Book People was founded in 1988, in the garage of chairman Ted Smart, and is now valued at £100m. Mr Smart's stake is worth an estimated £75m.

Mr Smart and chief executive Seni Glaister, who was just 21 when she joined the firm, are the sole shareholders in a business that now reaches two million customers through its direct mail business.

The two companies plan to launch a 50:50 joint venture that will combine The Book People's expertise in direct marketing techniques with Scholastic's children's brand Red House, which sells books through catalogues mailed to customers' homes.

The joint venture is expected to generate revenues of £8m-£10m in the first year, and Scholastic may increase its stake at a later date.

Dick Robinson, the chair man of Scholastic, said his business had been active in the UK since the 1960s, but that the "Harry Potter" effect on children's book sales had persuaded him that the time was right to increase the company's presence here.

"The UK children's books market is doing very well at the moment," he said.

"We want to sell more books to children and bring a love and passion for reading to a new generation."

Ms Glaister said she and Mr Smart remained "absolutely committed" to the business - despite their new-found wealth. "We love what we do," she said.

Using a network of independent sales staff, The Book People sells around 14m books each year, through a variety of book sales set up in venues such as office canteens, offering books at prices that are cheaper than those in high street stores.

As part of a wider shake-up of Scholastic's British business it has recruited a new chief executive. Ian Ronald joins from the direct mail retailer, The Wine Society.

Other well-known Scholastic titles include Postman Pat and Horrible Histories.